I suggest you be pleasant and polite to her and all the others at the school gate. Keep her at arms length and don't explain your actions, you don't owe her that. Don't text and block her on FB. If you get asked why? say you are too busy with DGD and don't have time. She needs to respect your decision. She can move on and so can you.
If she has an illness/disorder she needs to be encouraged to operate within the social boundaries the rest of us do.
Find another friend or better, friends. xx
Anger management!!! Help needed.