I think you should just act totally indifferent towards her; stop asking after her and minimise interaction with her, only converse with her when essential for work and keep it solely centred on essential work related matters. Avoid eye contact but don’t appear like you are doing so intentionally, act bored whenever having to speak to her and oblivious whenever you think she is making fun of you. If you briefly make eye contact with her when you realise she is mocking you just sigh, shake your head with a wry smile and just continue with what you were doing. Leave the room whenever she enters, but not so abruptly that what you’re doing is obvious. Continue this process for a couple of weeks and she will have little more to say to you or about you to others, you will cease to have a relationship with her.