Hi, that is is easy, you have two choices,
1st choice: you can block her on Fb and she will never see you again, she will think that you left FB. BUT if she logs in through another account she can see that you are still in FB, so that makes it tricky,
2 choice, you can create a group lets say (work boss) add herin that group and change settings in such a way that she cannot see your photos, updates on FB, status etc...she will think that you are not active on FB. This way even if you have mutual friends she will not be able to see your conversations with them.
Then after this you can live your life with no worries that someone is watching all your moves.