When Genesis represents her former roommate in a divorce case, against the man who secretly preyed on her twenty years earlier, is there a conflict of interest? Should she disclose the predation to her client, something she's hidden from everyone in her life, and that she's struggled to forget herself, as so many survivors of sexual abuse have tried?
As an ethical matter, I would disclose any past involvement with an opposing spouse to a potential client, no matter how long ago it happened. Here's an excellent blog post I found, when researching the duty of a lawyer to disclose an affair with opposing counsel or the opposing spouse:
Pontificating about ethics, when you're not the one in the trenches, is so easy.