It's your life, not hers. Clubs are great for some, and for others not so much. I would worry any time someone pressured me to join a club, however -- I'd investigate very thoroughly, for example, is this a religious thing to evangelize people? I'm also not sure why you see a nurse practitioner once a month -- they are not highly trained in anything and are adjuncts to physicians and other health professionals to handle minor problems. If you want talk therapy you want it with a psychologist, not a nurse practitioner. Essentially, nurse practitioner and physician's assistants are trained up to handle some of the minor things that busy doctors no longer have time for. If it's anything complicated, you will be referred to a doctor, or should be. That's why I'm confused as to why you're seeing one every month. Now, this club might be something she thinks would be good for you because of problems you're had in your life and could be a great thing for you, but again, make sure. More explanation of this relationship might help others give you better advice, including why you're seeing this particular kind of practitioner on a regular basis and what the club is all about.
Gosh, I'm sorry therapy went down like that. I have a 15 year old boy and while I think he'd benefit from not feeling alone and like no one else suffers like he does, asking him when he is in a spot desiring to work on himself to do what she is asking you is a bit much. Sounds semi self serving. However, there are a lot of therapists that believe and may be right that volunteering is a form of therapy. It makes us feel good. I know psychiatrists as well that have this as a recommendation to many of their patients and it can lift mood. Give purpose. Give much needed contact with others. But you should be able to choose how you volunteer your time. Asking you to be a peer leader in her group . . . hm. If that is not your cup of tea, it's not. No shame in that. And she wasted your parents money I guess going on about that. Personally, I'd have your mom give her a call. I'm a mom of a 15 year old son (did I say that) and while sitting in on his sessions isn't what I would do, I do oversee his care and I pay for his visits so have every right to discuss something like this with his therapist no matter what the therapist thinks. :>) (mama bear here).
Okay, reading further into your post, which always helps . . . I see she isn't providing mental health therapy to you.
So, let me turn back my original comments that I'm leaving just in case you are ever in that situation and saying this is actually a pretty awesome opportunity. I had my son volunteer at a camp this summer for severely disabled kids and young adults. Wow, what a learning experience. And he was not sure either what he was getting into. And some days were hard. BUT, he grew quite a bit from it. He had to step up. And he got to understand a bit more about life. And he got to be the person in charge and lead. All of this really helped his self esteem. AND, he gets to put that on his credentials that he will use this year to get into National Honor Society, fulfil a graduation requirement of service hours and eventually make his way into colleges. This would look great on your 'resume' so to speak as well. I would wonder if you couldn't try it to see if you like it. If you don't, then you can discontinue it. My son did the full week and then is doing a day here and there and will do a weekend day once or twice a month during the school year. HIS choice because he really liked how the experience made him feel. You might not. But then you know. :>)))