I trust the young lady will come through with flying colours.
My first thought was to Reaper, 'cause they sell sprues...
03032: Musical Instruments (12) ($6.99)

P14291D: Instrument Sprue ($0.37)
P14300D: Instrument ($0.58)
P14301D: Instrument ($0.80)
P14292D: Drum Sprue ($1.83)
P14310D: Drum ($0.4)
AND Musicians:
03098: Astrid, Female Chronicler

77078: Astrid, Female Bard ($2.29) as above in reaperbendyplastic
50198: Gallup, Zombie Survivor ($5.99)
50055: Sid, Rock Star ($4.99)

I don't often order from Reaper, but when I do I always kick in a few sprues of goodies...
Allow me to second Eureka's Jazz band, they are on my Want List, & different from Bob Murch's.

A photo I saw once seemed to show the instruments or arms with instruments as separate.

On closer view, perhaps not... Can somebody who owns this group unbuilt please confirm or refute?
As I see it, to get what
you SHE wants, you'll be converting base minis to musicians in costume.
Hope this helps out a bit.
Lili & I send our nest wishes to your brave daughter, and her stalwart family.
Valerik
EDIT: add Eureka pics