We don't know
However, what the book is is not important.
What the dialogue is intending to show is that Alina/Teri has completely turned her life around...the quote you gave is merely part of a longer piece which shows the context. Some additional extracts...
I know. I got it from a used book store. The guy there recommended it to me. It’s good. I got a job too. Like a real job with real hours and stuff.
When they gave me my stuff back at the hospital, there was this envelope with my name on it. Almost ten thousand dollars inside and a ticket out of town. I don’t know, probably hush money, right?
Who cares? A new start.
Well someone once told me I could be whoever I wanted to be.
Basically, before, Alina was merely an uneducated prostitute with minor aspirations to a singing career. Now she has a job, is improving herself by reading and has a positive outlook.
The point of the scene is to show how effective Robert's actions have been.