That is quite a dilemna. I really feel unquailified to weigh in, but in true DIS fashion, I am going to anyway. It seems like this is a lifelong dream of hers. I always think people should go for their dreams, but agree with Princess that you should not go into debt to do it. If you could comfortably invest your time and money, I would say do it. The sooner, the better. I know Fran has a lot going on right now with her injury, but this could get her mind off that and onto something else. At the same time, the potential stress this could cause (expenses, time, getting a new group together, rehearsing, etc) would just add to the stress she is already feeling with her recovery.
It really is a tough call. I guess my determining factor would be how do you truly feel about it? If you are not into it, I do not think it is fair to drag you through the unnecessary stress. DH and I have things that we do together and things that we persue separately. She should go after it on her own if you are not into it with minimal input from you. There is a balance between supporting her and putting what you want aside for her. All of that said, I think it sounds really cool. Getting a tax deduction for doing a wonderful thing sounds like a dream come true. I hope she gets what she wants, and you get what you want. If those wants are different, hopefully you can meet somewhere in the middle.
If you both want the band, I would love to hear something down the road.