Oh wow, this is a tough position for you.
In all honesty, I really think she is being unreasonable - that is a massive amount of money to pay for a hen do - I wouldn't go at that cost.
Also - 3 hen do's? I can understand 2 - one weekend, and one night out at home for people who couldn't go to the weekend, but asking you to organise one for her family is a bit much. Regarding this, I would suggest combining them - maybe do an afternoon tea for her family, followed by the night out with friends?
But back to the costs, I think she needs to rethink this completely. Is she going to be happy about the fact that only 6 people can go? Better to do a cheaper weekend in the UK that everyone can afford! Or have you already got flights and accomm. sorted? Honestly, I really think she needs to at the very least pay for her own flights and accommodation - none of this loan malarkey, seeing as it was her choice to change it all at the last minute and make it so much more expensive.
Are there any other bridesmaids that can split the costs with you, or will her family pitch in? I'm guessing the other Hens aren't up for it as they're forking out so much already.
I'm sorry I can't really offer any more advice, just lots of sympathy for you, I hope you manage to work something out! X