That’s a difficult situation. Good point – maybe additional time spent with your mother can help. Of course, daven.
Not to pasken at all, but food for thought; please do not take this advice without asking a rov if you should say it to your mother. But – perhaps if your mother discontinues such a friendship, it will be a zechus for your refuah shelaimah. Maybe that can motivate her?
Hatzlocha and besuros tovos.