It is her choice to stay. In my eyes, if a spouse wants to stay despite infidelity and anything else that is a struggle, then it would make sense to work through it with a skilled therapist, one that specializes in repairing any rift that would have developed and help both individuals bring themselves to a healthier more functional place as they rebuild a future together. I'm not talking about frequency of sexual relations but a rebuilding of trust, communication and intimacy which includes emotional intimacy. Learning to let go of resentment and learning to forgive, not just their partner but also themselves as infidelity is certainly a blow to oneself.