Considering she felt justified for being abusive towards you with her apology, that sends up a huge red flag. I think it's a matter of time before she does it again.
I would really start thinking about keeping contact to an absolute minimum, if at all, given the nature of the apology.
I agree with Dee in that it's fine to break the promise if it's hurting you. I don't think your mom would want to you to keep that promise if it's hurting you either.
