I wasn't suggesting that you were struggling to get laid ... but it's a rare chance to be able to do it with no emotional risk, knowing that she's likely to let you off the guilt hook by running back to her abusive boyfriend. I don't know the circumstances of what you are describing about yourself, but a girl who keeps running back to a cheating boyfriend is pretty predictable, don't you think?
Even if I'm wrong, and she is finally fed up with her ex-to-be ... that's even worse. You know the extreme pain you can cause by encouraging a one-sided romance in the name of friendship, yet that's all you are offering her. This is precisely why you plan to bail out if YOU start feeling something for HER. I don't see any possible win-win result for her in this ... at best, she is trading abuse and heartbreak for abuse and heartbreak.
Carl.