If this helps, when I got Minthara in Act 2, she didn't do a whole lot after the initial quest to get her. But I don't know if that's a bug or if it's because, depending on when you get her in Act 2, she might not have much to say (if you get her at the beginning vs. at the end of Act 2, etc).
I can say that in Act 3 she reacts a lot more. She approves and disapproves of a lot of decisions, she has things to say about decisions that are made and situations you find yourselves in.
So I don't know if the Act 2 thing is a bug and she's not reacting, or if she just isn't given much to do in Act 2, but does more in Act 3. Figured I'd share my experience, all the same.