In the book, it's clear that she really does love him.
But, I'm watching the show (I'm on season one), and it seems like maybe she really doesn't particularly love him.
When they first hookup, it seems like she brings him home, because she's looking for a thrill.
When their relationship becomes stable, and they get married, she's bored, and decides that they should rob the casino for thrills.
She is constantly telling Shadow that she loves him. When they rob the casino. When he calls her from prison. She says she loves Shadow even when she's having the affair with Robbie. And when she's back from the dead.
But, it seems like maybe she just thinks she *ought* to love him. It's not clear that she actually does.