Honestly, they are giving her some control which is very important when you have a disease that gives you basically no control over your life. There isn't a huge difference between upping the dose or changing the frequency - both work. Hair loss could have been Remicade in the past, though it could easily be malnourishment or even active disease.
It sounds like she has trouble with IVs which is why she wants to do the higher dose. That's not a bad reason. As long as she is doing it with her eyes open - remind her she had hair loss which COULD have been caused by a higher dose of Remicade - then I think it's perfectly fine for her to make the decision.
You can also do a pros and cons list with her for each option - that will get her thinking about both options.
Teens are given more control around 15-16 because in a few years they will be making the decisions. Like it or not, we have to let our 18 year olds (who are really still kids) make all the decisions once they turn 18.
My 18 year old was VERY stubborn and refused a feeding tube. We watched her weight fall lower and lower - she had already been underweight and she was losing more and more. Nothing we said got through to her that she needed the NJ tube. She absolutely refused, even though she was so underweight and exhausted, she could barely do anything and was in bed most of the day. Since she was 18, all we could do was watch her get sicker and sicker and try to make her understand WHY she needed the tube.
Finally, when her doctor told her that her organs could fail if she lost more weight, she understood how serious the situation was, and agreed to the tube.
As parents, it is our job to teach them, starting at 15-16, how to manage their own healthcare. That means knowing their medications, filling their own pillboxes, and helping you make decisions. When the GI gives her the choice, then it's your job to help her think through the options and figure out which one is best for her.
She will be doing this all on her own at 18, so from 15-17 you're really practicing for that. Once she is 18, there will be bumps in the road - some big and some small. She will learn from them and hopefully you will be there to help her when she makes the wrong decision, which she will from time to time.
But right now, at 15-17, it is your job to prepare her for taking over her own care. That means thinking about everything that could be impacted by IBD - including her diet. Understanding WHY she can't eat fried food and sugar all day.
Her decision actually does make sense to me because it sounds like she has tricky veins which are probably scarred from so many infusions. You don't want them all to get scarred, so less frequent infusions make sense.