Way I see it, it's perfectly feasible for her to have friends (or, if "shyness" is her primary character trait, "people she hangs out with when doing her things") in her "sphere of comfort" which would be music. At school or elsewhere, not so much.
Knew a few people like that - toss them into the right environment and they are the life of the group, take them out of it and they become unacknowledged wallflowers.
That would make for a fun opportunity to have her butt heads with Hana as direct competition in some way.
The ultimate confrontation ending up, of course, broken up by MC's magic dick. /s
Edit: Or, even better,
Hana: OMG, my favoritest artist did a homage to my H-scenes! Squee!
Juliet: Wait, the original is yours?
H: Uh... er... maaybe? You.. um... know that kind of stuff?
Juliet: Yeah, I drew -this- one.
Hana: Nani?!
Everyone else: Oooh!
MC: Now kiss.
Will write script snippets for free, Runey. Just sayin'
Edit2: Though, honestly, I think a rockin' guitar player/vocalist would be best. We already have Hana as the visual arts type, but no musicians. Making Juliet a star of self-assertiveness on-stage and a complete dork outside tickles my personal fancy for trope-breaking.
Not to mention this opens up the possibility of MC getting involved in helping her overcome her shyness in daily life. Boring solution - make her do exhibition stuff or concerts with controlled vibes or whatnot.
Awesomesauce solution - appoint Maria her assertiveness coach.
MC: "Just tell her no if she gets too handsy"
J: "Wait... what do you mean too handsy?"
M: "These are as awesome as Ellen's!"
Then you have all the potential self-assertiveness exercises Coach Maria can come up with. Nuff said