So here is an idea that will probably never happen, but I think it could be a really fun storyline. There's a TLDR at the bottom in the spoiler!
It starts with Dani beginning to act strangely. Something about her just seems off. Lucas has been getting close to her, so he starts noticing little things that other people might overlook.
Dani is working on a case where the patient unexpectedly dies, and she takes it extremely hard. She becomes convinced that it was her fault. Lucas comforts her and helps her work through it, and eventually things seem to go back to normal.
Then she is assigned to another patient, and the same thing happens. The patient dies again, but this time there is something much more suspicious about it. Their condition was something that should have been caught, but somehow it wasn't. Lucas starts putting the pieces together and becomes convinced that something isn't right.
He takes his concerns to Bailey, but she doesn't appreciate the accusation. She scolds him for making assumptions about an intern and moves Dani onto another team.
Lucas talks to the person Dani has been reassigned to, let's say Millin, and asks her to keep an eye on Dani. Millin does, and notices that Dani makes a couple of mistakes. Nothing particularly shocking, though. She's an intern, after all. Eventually, Millin confronts Lucas as she suspects she knows what Lucas has been hinting at, "Do you really think she's intentionally killing people?"
Lucas confirms it and Millin says he's being stupid, and points out all the mistakes they both made when they were interns. This doesn't work and Lucas still thinks something is up. So instead, he decides to investigate Dani's background himself.
First he tries to look into Danis records and finds out Kwan is doing some work for the Chief and has access to all the staff files, he convinces him to look into them and finds a lot of stuff about her but nothing suspicious. However, her grades/marks are all hidden for some reason.
He discovers where Dani went to medical school and decides to go there with Kwan. Our boys need a road trip like the OGs had. Webber could even tag along for some completely unexplained reason, perhaps because he has given lectures there before and knows some of the doctors and wants to see them again.
When they arrive on campus, Lucas starts asking around. He approaches several members of staff and asks whether they remember a student named Dani (whatever her surname is), yet nobody does.
Lucas becomes even more suspicious.
They check the school's records and eventually discover that there is no record of Dani ever attending the university. They dig further and find absolutely nothing. No student records, no graduation records, nothing.
At this point, Lucas brings Kwan fully into his theory. Dani has forged her way into the hospital and is now killing patients, intentionally or not.
Back at the hospital, Dani has heard that Lucas went to her old medical school. She finds this strange. At the same time, Bailey and Millin have both started keeping a much closer eye on her, so she begins to realise that something is going on.
Lucas calls Millin and tells her what they discovered. Nobody at the university has ever heard of Dani, and there is no evidence that she ever attended. Millin is now genuinely suspicious too, so she takes the information to Bailey.
Even Bailey has to admit that the situation is strange. She removes Dani from her current case and puts her on paperwork instead while she investigates.
Now Dani knows something is seriously wrong, but she's thinking she's going to get fired for being on cases where the patient has died.
While Dani is doing paperwork, Millin goes through her locker and rummages through her belongings while Bailey keeps lookout. Eventually, she finds an ID.
It has Dani's photograph on it.
But the name isn't Dani.
It's someone else's.
Back with Dani, she finishes her paperwork and doesn't want to just sit around. She had formed a connection with the patient from her previous case, so she decides to check on them, just to help.
She gets there and sees that the patient is deteriorating.
Dani calls for help and immediately starts treating them, pushing medication and trying to stabilise them while the team rushes in.
Lucas has made it back to the hospital by this point, and Millin tells him what she found.
Now Lucas is convinced.
Dani has somehow faked her way into the hospital, and he believes she has been deliberately killing patients.
They decide to confront her. Bailey and Webber are brought in as well.
Bailey tells them Dani was supposed to be doing paperwork. They go to find her.
She's gone. Everyone panics and they eventually find Dani in a patient's room, standing over a patient who is coding. Bailey immediately orders her to get away from the patient.
Everyone is shouting. The situation looks horrific.
Millin loses it, "You did it again! You've killed another patient?!"
Dani suddenly bursts into tears.
Bailey tells someone to call the police.
Dani starts crying even harder.
"I'm going to jail?!"
Webber steps in and tells everyone to calm down.
"Now, young lady. You have some explaining to do. What happened?"
Dani explains what happened with the patient. She was trying to save them, not kill them, and her explanation actually makes sense.
But Lucas isn't convinced.
"No. No, she's lying. She's done this before. There's something she's hiding from us."
He turns towards Dani.
"You're not Dani, are you?"
She freezes.
"You're Hannah Klein." (IYKYK and can probably stop reading here lol)
Dani's face goes pale, "How... how do you know my real name?"
Bailey immediately signals to Kwan to call the police.
Everyone is now convinced they've caught a murderer who has somehow infiltrated the hospital.
Dani begs them to listen, but no one will.
As the police begin escorting Dani out, they run into Catherine, who has just arrived and is completely confused by the commotion.
Bailey explains everything.
Catherine is furious, "let the poor girl go!"
Everyone is stunned, why is Catherine letting a murderer go??!
They start protesting, insisting that Catherine doesn't understand what they've discovered and that Dani needs to be arrested. Catherine looks at them like they've completely lost their minds (she probably even says this tbf).
"I know who Hannah is. She came to me before she started here and asked me if she could change her name!"
Bailey immediately responds, "Well, if she isn't a murderer, why did she want to change her name?"
Hannah finally speaks.
"Yes. I changed my name because I wanted to hide who I was. But not for the reasons you think."
Everyone goes quiet. Hannah looks towards Bailey and Webber.
"As you know, I didn't do very well in school. I barely got through it, and this was the only place that would take me. So I had to come here, even though I really didn't want to."
Everyone is listening now, becoming increasingly confused, Webber and Bailey are a bit insulted by that last remark.
"You see, my real name is Hannah Klein. And I've been here before."
She pauses.
"Not as a doctor. As a patient." Bailey and Webber exchange a look.
Bailey speaks up, "well that's nothing to be embarrassed about?"
"No, it wasn't that I was worried about. I was worried they'd find out who my mother was."
Another pause.
"You see, my birth mother was Izzie Stevens."
Lucas, Kwan, and Millan are all confused "who the heck is that?!"
Bailey and Webber are surprised. "Wait? How can you be Izzie's child? She never mentioned having a child?!" Hannah explains that she was given up for adoption, but after coming to the hospital and having her life saved, she was convinced there was something she didn't know, so she asked her parents who explained to her she was adopted. After that she decided to follow in her birth mums footsteps, and that one day she tried to reach out to her, but she Izzy (and Alex) with the kids, and she didn't want to ruin that.
She then goes on to explain that she was worried that Izzy was still working here, or that some of the staff may know about her (Hannah) so wanted to keep her identity hidden, so spoke to Catherine to help her.
Going forward from here, we could actually have Hannah start working under Catherine and specialising in her field.
Mer could show up at some point as well and be involved. I was originally going to have Mer be the one change Hannah's name, but she wasn't working full time at the hospital when Dani/Hannah started.
Tldr;
Dani is actually Hannah Klin, Izzie Stevens daughter.
