We are having a DW, with only our immediate families invited. I was figuring/hoping that my sister wouldn't be able to afford to come, and I was totally cool with that. But, of course, my parents are helping her. Like they always do.
We were all going to buy plane tickets together (my mom's idea). The tickets dropped a few weeks ago - $250 less PER TICKET. My mom and I were ready to buy... My sister wasn't. My mom said we had to wait. Now they're back up again. $150 more than they were two weeks ago. Why does my sister have to ruin things, and why does my mom enable her? Ack!
(I have to go along with my mom's plan, because she will be keeping my daughter with her and coming home before my fiance and I do. I'm paying for my daughter's ticket, but it needs to be next to the seats that my mom buys.)
If you & your mom can agree on a flight, you can buy your daughter's ticket before she buys hers and change your daughter's seat online later. You could also buy your daughter a refundable ticket and change it once your mom books hers. Most airlines have a $50-$100 change fee if you need to switch flights. Still cheaper than letting the good sales entirely pass you by.