It sounds like one of the following things are happening:
1) She’s being selfish
She’s just using your generosity and warm body to fulfill her own need for attention or soothe her loneliness.
2) She’s confused
Perhaps she legitimately doesn’t know what she wants. Maybe she likes you but isn’t sure you like her. So she’s making herself SUPER available. Or more likely, she is not completely attracted to you but thinks she might GET attracted to you…in the dark.
3) She’s a dummy
She’s just dumb, man. She thinks that’s appropriate, acceptable behavior and it doesn’t even occur to her that this messes with your head and your boner. Dumb!
4) She’s DRUNK
Showing up hella late, uninvited, stripping down to her skivvies, getting into your bed, slurrin’ some dumb shit like, “I’m…I’m soo not trying to have sex with you, I swear! I’m just like, fuckin, not interested in sex, you know? You’re such a good friend. You’re like, the best”. Gross.
I would not recommend pursuing anything romantic with someone like this. The next time a girl is sincerely interested in you and she is potentially someone worth dating, I think she will make it more clear that she is interested. Certainly more clear than this bozo.