Dealing with an annoying coworker sucks she's trying to bully you into having a relationship with her.

She's obviously not going to take a hint. I'm curios about what you said about about her barging into your office. If you have an office it's not ok for someone to barge into it friend or not. Only the boss can get away with that *****

Saying things you afraid someone doesn't want to hear is never easy. The truth is they may get hurt or even angry, but you have to take care of yourself first and foremost. If this coworker seeks revenge by lying about you I would confront her about the lying, and if that doesn't work, go to HR?

The same with your cousin Sarah. There is a way out. It's called honesty....and it's hard as hell to do. You may hurt her feelings, but again you need to take care of your needs. If you don't ...who will?