Sending Prayers for Jessica. She sounds too young to be going through this
I too would see if there is another specialist that might take your concerns more seriously.
At this point I would suggest as well as above a trial run on a gluten free diet. Plus no alcohol, no sugars. She needs to be on this for at least six wks to see if this might help.
I am not familiar with this PVNS at all. But I am all to0 familiar with joint swellings et al, as I have had RA since 1995.
Swimming, even if one can only walk in the water, or do some sculling is very helpful. Also even very mild bicycle work - by that I mean very low resistance on the pedals.
Yoga is wonderful - a theurapeutic kind, along with breath work and meditation.