To me, poly isn't the issue here. Do you want to give her another chance? She could earn back your trust, or she could hurt you again (by cheating again or by something completely unrelated). No one can decide for you if she and the relationship are worth taking the risk.
Poly becomes a secondary consideration. IF you want to give her another chance, are you willing to try the relationship structure she wants? If it's not something you're comfortable with, that's valid. If you're willing to give it a try and see what happens, being aware there may be even more emotional pain down the road, that's cool too. Try not to think about it as "punishing" or "rewarding" her- At this point it's not even about her, it's about you.
Just like a mono relationship, you've got to decide what you want out of the relationship, what effort you're willing to give and what your boundaries are. Poly just has this tendency of bringing those things out in the open, since the mono assumptions that a lot of people rely on go right out the window. It's possibly more complex and more challenging, just because you're dealing with multiple people's needs, but at its core poly is the same as mono- it's about your relationships with people and how you manage them. The rest is just trappings.
ETA: I do think she needs to work on regaining your trust before she tries to manage two relationships. Right now it doesn't sound like either relationship is particularly stable and that's just going to make things harder on everyone.
Pan Female, Hinge in a V between my mono (straight) husband, Monochrome and my poly (pan) partner, ThatGuyInBlack
Last edited by ThatGirlInGray; 01-31-2012 at 11:48 PM.