ABANDONED. girl who writes a play in a convent school

[Christie]

I'm looking for a book about a teen girl who lives at a boarding school in a convent (I think it's a convent.) and is a writer. There is something to do with a mysterious "blue" lady/nun/ghost. The girl's play is not chosen to be the school play. Her enemy's play is chosen and she has to work with her. The mystery of the blue lady is solved in the end in the school's garden, I think. For some reason, I recall that the refectory is a main setting in which action takes place. Thanks to any who can help me locate this book!!

[Danielle]

Is it Gilda Joyce and the Ladies of the Lake she wries a play but she gets to preform hers and she is at a Catholic school.

[Christie]

Thanks for the recommendation but that's not it.

[Lobstergirl, au gratin]

Any idea when this was published?

[Ann aka Iftcan]

OP hasn't been active since just after posting this (her reply to Danielle's suggestion was her last activity.). I've sent a PM. If no response, the next Mod to check this thread can move it down to abandoned.