Sorry you are being harassed this way. Depending on where you live, you may be protected under the law against sexual harrasment.

I know being touched, approached, or just observing sexually charged situations can be really stressful. It sounds like you might be emotionally flooded during these encounters. Maybe go find a quiet place after she flirts with you and ask yourself what you are feeling. Are you angry, frustrated, aroused, embarrassed? Then check in with your body. Are you hungry, tired, etc. Then come up with a plan of action to fix the situation. She's not going away and probably won't change, so you need to find a way to deal with her and take care of yourself.

You are brave to talk about it. Sometimes you just need a place to get it off your chest.