I've had pretty much all the comments here too!

I usually say "I'm not trying to be your friend, I'm your Mummy ...". The party one stopped when I pointed out if she wanted a cake, etc, it probably wasn't a good idea to leave me out.

This passes - next stage is "but (my friend's) mum let's her/has (whatever)", to which I respond with the a somewhat heartless, "well, that's their family and if you go and live with them then you can too, but not here!"

Try not to let it get to you.