There is a song called "Don't Call Me Trailer Trash (I live in a mobile home)" that might not necessarily be age appropriate, since technically the character would be in her 20's, but it is a great character piece.
Stay away from Les Mis for any and all college auditions.
Maybe go old school..."But not for me" not obscure, but I guarantee not many teens will be singing it.
"My New Philosophy" if she is more belty...
I would assume by "Age appropriate" they aren't necessarily saying the "character" needs to be a teen...just not blatantly an adult...I could see them being off-put by "Someone Like You" purely because Lucy is a prostitute, but it is narrow minded.
Another question would be how young does your daughter look? If she is a mature kid, but really really looks young, that could be another issue as to why she is getting these comments.
Also go to a local music store and find the Mezzo "The Singer's Musical Theater Anthology" there are numerous volumes and always have a great range of popular and obscure.
Baritone in search of a role in a new musical...