When she was in Room, Ma coped by creating a routine, a mask of normalcy, that served to block out the actual horror of her situation. Ironically, when Ma leaves Room, she is forced to confront Room and her trauma. This is evidenced by the talk show scene, where Ma is asked questions that -- while eloquently answered -- we never saw her having to think about in Room. So perhaps Ma's suicide attempt is, at its core, simply a response to fully realizing what has happened to her (of course, we can't really ascribe a logical chain of thought to this situation, and it's probably more a confluence of factors that push her over the edge).
Another thing to consider is that Ma had never raised the questions that had been asked of her on the talk show, and her suicide attempt is perversely fueled by her desire to help Jack. I'm referring specifically to the question about giving Jack away. Perhaps Ma felt that she couldn't parent Jack now that she was out of Room, or that the "professionals" could help him better than she could. We discussed how Jack's tether to Ma was limiting his adjustment to Outside, and how the silver lining of the suicide attempt is that Jack had to learn to run before he learned to walk (so to speak), so in a sense, that line of thinking might not be too far off the mark. Of course, the idea that Jack would be better off without Ma borderline ludicrous at best, because her death would traumatize him. But it's understandable that Ma might come to some of these conclusions in her severely depressed state.
I also wondered about how Ma never attempted suicide in Room. She had access to knives and pills, and it could be days before Old Nick checked in. It's possible that she considered suicide on some of the days when she was Gone, but couldn't do it with Jack there (I think there's a world of difference between killing yourself and killing yourself in front of your child). However, there were two comparably horrendous years in which Ma didn't have Jack to serve as an anchor, so if she was going to kill herself, she probably would have done it then. This makes me think that Ma didn't consider even suicide until after she got out of Room.