OH NO WAY! I'm shocked by some of the responses here and wonder if they are from PITA MIL's who put the same pressures on their DIL's and sons? I have a MIL that is also pushy and brings things up over and over.... her AND my FIL have pulled many things to get what they want like - if they don't get the answer they want from me, they corner DH and ask him seperately - like playing us against each other. It has put quite a strain on our marriage at times. The good thing here is, it sounds like you and DH are on the same page. If you guys were asked, and you said NO, because of XYZ, his mother should DROP IT! His mother needs to respect that he is a grown man with a family of his own to worry about, a job, and that unfortunately, this time the whole thing just doesn't work out.
Don't feel badly, stick to your guns, otherwise - she's always going to try to control your marriage and family. You have to always let them know that you guys are in control of your own family and plans.
To previous posters, I don't think this has anything to do with respect of older generations.... you can't ever keep everyone happy, it is a financial issue, a time off work issue, and frankly in this economy there is no other justification needed. What is she supposed to do, turn around and tell her kids they have to cancel their long awaited Disney trip to go to a reunion where the kids will not know anyone?
Family is very important to me, but frankly, my husband and I are OVER bending over backwards to accomodate ridiculous demands of family instead of keeping our OWN immediate family in first priority. I love my family and if I can do anything for them, I always will, that being said.... my husband and daughter come first. Hopefully I won't get flamed for my stance!