It's cheeky of her to ask in the first place and to be pushy when told no, is really out of order. My friend's grandparents used to make a big Xmas dinner with a couple of turkeys from their farm which I thought was very kind as they'd cater for a lot of people and their partners, kids etc. They were also very generous to send everyone off with a box of leftovers, only leaving a bit for themselves to enjoy as sandwiches without having to cook over the next day or so. SO I was horrified to witness one of their nieces, who was married with no kdis, wealthy and in her 40s, notice there was some meat still left over after and ask if she could take it for her pet as well. And got a bit funny when someone said they've been generous enough, don't push it. I was fuming she made them feel awkward after all their kindness. My point is, some people will take the mick if you let them. Say that if the boyf comes, you will have to extend the invite to daughter's boyfriend. husband's niece, etc. etc. or it will cause offense and you need to keep the group small. Be nice but have the attitude in your head that she can take it or leave it. Don't get angry or be provoked, as she will look for you to do that so you feel guilty and eventually relent.