You're not being mean at all! I'd feel exactly the same way. If you are worried about DH going back on his word, maybe he could be the one to tell his mum initially so that you show a united front from the beginning. If she does raise the issue, maybe think of an alternative time that she could come (be it a few weeks or a few months later) so that she has something else to focus on (not that you have to, it's just covering your behind!) and then maybe recommend some places she could stay. I suppose what I'm trying to say is that she will want to come out at some stage, so try to be prepared with a response so you get what you want