Just tell her straight out NO she is not to attend. She doesn't care about your feelings so why do you care about hers? Plus you will have a baby soon and she'll want to enforce all sorts of weird ideas about raising your child and yet again you'll have to say No to her for all sorts of things. So if she gets used to you sticking up for yourself now then down the track life maybe easier and you'll both know where you stand.

Sorry I have been so direct but I used to allow people to upset me and take my personal control away, but since being a mum I've learnt too stick up for my own needs and my kids.