spanky you really shouldn't give in to her, which is what keeping them off would be.
Why the hell should your DC LIE about sickness because of (a) HER and (b) the school's piss poor security up till now.
No WAY should they have been granted access to the DC during the school day, nevermind alone in a room.
I hope that you read them the riot act.
Go to the school this afternoon, speak to the HT and warn them that there may be a risk of her trying something. Reiterate that she is not to have ANY contact with your DC whatsover and that the school MUST treat any appearance by her as that of a hostile and dangerous stranger. They must call the police if ANYONE is seen hanging around, trying to engage with children in their care, or attempting to gain access to the premises.
Can you please ask your DC to immediately tell a teacher/dinner lady/HT if they see their GP?
mrs happy to have you here! You don't need to make big statements to them. You knowing that you don't want them in your life anymore is enough.