What would I do vs. What should I do

Of course, a lot would depend on how well the girl and I knew each other and the age of the girl.

I want to pick #4.

But #2 is more reasonable in today's messed up world. Not only would I explain about the possible legal troubles, but I would want her to absolutely know that her sexual feelings are good and healthy. I would not want her to feel as if I rejected her or that her sexuality was a bad thing.