This Rosa Parks thing is rather confusing. What is that about?
OP, can you try to imagine her as someone who wouldn't entice you? Try to think of her as a person with a raging STD or as a person who is not a woman but a man dressed as a woman or as someone who is really ill or as if she were your own daughter or as simeone with a weird toilet fetish. None of those things have anything to do with one another, but throwing something weird in there might make you see her as a person instead if an object of lust and that might allow you to see past it. You've gotta take her off the pedestal so that you can interact with her in a normal way.
We've all had tempting thoughts about others -- students, teachers, colleagues, friends, whatever...the trick is not to dwell on those things or feed them. Sure, she may be lovely, but she is also a person with flaws and issues and maybe you can imagine them (or anything else that takes you out of your current attraction) to get out of this mess.
Sorry you're in an uncomfortable situation. Hopefully, when the semester is over, the issue will disappear....
"He who accepts evil without protesting against it is really cooperating with it." -Martin Luther King, Jr.
"We first crush people to the earth, & then claim the right of trampling on them forever, because they are prostrate." -Lydia Maria Child.