I know money can be a touchy subject for some people. However, if this particular bride's maid is having trouble committing because of money (besides her being difficult with the dress), you can give her the option now to not be in the wedding party and attend your wedding as a guest. That way she won't be stressing you out as much and she can book the trip whenever she wants. Best thing is to have a chat with her in person. Again, it is your big day and you still have a lot of time to work any issues out.