Don't feel bad about failing in the female friends department. You haven't, dont worry. You have plenty of female virtual friends here :~) lol
One of the sayings that I keep near to me is, 'People come into your life for a reason, a season, or a lifetime'. I had to learn the hard way who some of my 'seasonal friends' were. I have actually lost someone as a friend who I grew up with as well throughout this planning process. She was causing me waay to much undo stress during what is supposed to be one of the happiest times in my life.
What seems important to us as brides, are defitenly not some of other people's priorities (regardless of what they may say) But, I defitenly agree that you should talk to her and explain exactly how you are feeling. Especially since she has already booked her trip.
Hope this gets straightened out :~)