You will have to come to an even comprimise....OR....
I'll tell ya what might be better...the part of the trip that you have agreed you wanna do togeather, do togeather, but the part of the trip you are disagreeing on, maybe you should split up for a while and meet back up a couple weeks later? This is your trip and you should be able to spend it the way you want to, if you cave and end up doing what she wants to, then i for see a battle at some point on the trip...I have been there i know first hand. Now if she caves and you end up doing what you wanna do, you can also expect a battle at some point along the way. I think during the time that you are relaxing in Autria or Italy, she should go and what she wants to do....neither one of you want to be accused of ruining the other one trip.
This is a very difficult situation and its this type of thing that caused me never to travel with friends, but i did not find out until we were half way through Cuba...we ended up going our seperate ways over there and and are not the friends we were before it happened. <_<
I really do hope all works out for you, and that a mutual agreement can be found B)