I disagree about removing her from your life. Here is a person who has loved you more than anyone else. Why would you want to take away that love? She obviously still cares a lot about you.

She could play a role in your life, a very important role, but that role needs to be managed.

My suggestion is to relate to these thoughts in a different way. Rather than hating them and trying to drive them away, my suggestion is to simply acknowledge their presence, and examine them. For example, you could say to yourself:

I do not consider you or these thoughts to be sick or anything else that you have called yourself. I think of them more as transference, akin to the transference that people sometimes have for their therapist. This could be maternal transference, it could be erotic transference. It is a normal phenomenon that just needs to be managed.

With regard to daydreaming: have you done any meditation or mindfulness work? In meditation, the mind inevitably wanders. The solution is to bring the mind back without judging yourself. So if you find yourself daydreaming about her, simply bring your mind back to whatever you were doing without judging yourself. Simply say daydreaming and go back to what you were doing.

Stop judging yourself for caring about someone who gave you more love than anyone else. Instead, simply acknowledge It makes sense that I think about her, she was and is so good to me.

This is a very insightful comment, as is the following one:

What could be done to improve your life, such that daydreaming about her feels less needed?

ETA: I think the goal is not to destroy the thoughts but to see them gradually fade away as you come to grant them nonjudgmental acknowledgement, come to understand their function in your life, and come to improve your life overall.