It is kind that you offered her shelter in crisis, but if you are not up for this kind of support long haul, it is totally ok to NOT be. Could be a friend and guide her toward appropriate aftercare and then step back and deal with your own break up processing.
Could not be telling a recent sex crime victim you don't find her attractive. Even if it is true, you can keep that data to yourself. There's other ways to be firm and NOT start a romantic relationship with her.
Could keep it simple, short and sweet.
"Thank you. I appreciate you and your feelings and I care about you as my friend. But this is totally NOT the appropriate time to be thinking about big life decisions like starting a new romance together.
1) You were just sexually assaulted.
2) I just broke up.
We are both having to process some other heavy Life Stuff first. So let's do that and keep our relationship as (good exes and friends) at this time."
Focus on being a friend and focus on HEALING appropriately first (both of you.)
And if she wants to float off into dream world so she can escape her current reality? You could...
- Redirect her to the friend space with you. It is NOT romance space here.
- Encourage her to get appropriate aftercare after her ordeal and not go all dreamy. Provide links to resources, ask her what she's done to follow up doctor wise, report a crime wise, etc.
- Maintain your own boundaries. If you have to, call her parents, sister, brother whoever... to come and care for her so you can step back in good faith because someone else is tending to her that is more appropriate than you at this time.
You might be good for initial shelter person, but you are NOT be the guy for ongoing aftercare person. You are not at that place emotionally right now and you don't even sound like you would want to be even if you were emotionally well.
So... could respect your own limits. You are not emotionally well right now yourself. And you have no desire. Not able. Not willing. Limit reached.