Hi hvmontigny & welcome!
You know, 13 is such a tough age. It's when kids start to express their individuality. It's when they seem to act out the most. They have left their elementary years, and now they aren't quite highschoolers, but stuck in the middle. It's sort of like turning 20. You aren't a teenager anymore, but not quite an adult. I hope I'm making sense here.
What things is your daughter losing interest in? I ask because she may just be changing her interests. Don't get me wrong, you are right to be concerned about loss of interest. However, maybe she's just growing and changing? Just a thought.
I struggle with motivating my 17 yo son to do his treatments. Look up stubborn, and there will be his picture! LOL Teens just seem to feel that they are 10 foot tall and bullet proof. I know I was! LOL I know if I sit & watch a show with Jordan during a neb treatment, he seems to do it better. He doesn't feel secluded that way. I think luke may have hit on something when he mentioned that your daughter might feel alone in this fight. As much as teens want to feel independent, they still want and need us.
Definitely encourage your daughter to continue her treatments. Don't be too harsh though. It may make her even more determined not to do them. Try to stay positive about it. I know that isn't easy. Good luck, and hang in there.
Stacey