Vengeful ghosts in the theatre... what do they do?

Have mirrors and make your characters see things. That would be weird and funny.

Her mother abandoned her and so mothers of actors that come into the theather start feeling strangely uncharitable towards their offspring.
The last thing she saw was a half-pulled velvet curtain, up in the ceiling, so curtains keep rotting.
She was just going for a walk in the country when that happened (or at some point in her future, which she didn't get to) so moss and grass and wet stains appear in ceiling and corners.
Her dog died of hunger because it had no one to feed it, so all the dogs that get near her start sniffing around and begging for food, and doing all the tricks her dog used to do for her.

Any use?

Someone in the theatre "breaks a leg" - awesome!

You can look up the stories of the various haunted theatres in London's West End. In one case, a headless man appears regularly to those in balcony seats - he's seated in an orchestra seat, with his head in his lap. I think one also sometimes sees a hanged figure, just off stage.

How much of your haunting do you want to be "residual" - like, images of things that happened in the theatre - and how much of it "poltergeist" - things moving around or coming untied, and ending badly?

wow! thanks for all the feedback, guys! I really appreciate it! Keep the ideas coming!
And serotonin, to answer your question, I'd prefer most of it to be more poltergeist-like things happening, like objects moving around, etc.

Thsi si going to sound a little strange- I actually worked in a "haunted thearte" when I was in highschool- the story was that an outsider--- kinda a "reject"- he used to skulk in corners, and was rejected by a lot of girls- hung himself from the balcony railing in the 60's. Personal experiences range from phantom smells- the kid's hair pomade was among one of the most popular expressed- to actual full body sightings- I was in the basement one night late working on costumes for a production and turned around and he was walking past the door- I thought it was someone wandering where they shouldn't I was alone in the bulding and the doors were all locked. I went and looked for him and couldnt find him and the next day, I asked Deke (the director) if he'd let anyone else into the building before he left. Deke got this funny look and pulled out an old yearbook, and sure enough, it was the dude. I also had things moved, and the railing on the balcony would bend- it had to be replaced twice while I was there. OTher people reported that they'd be in the basement (the costume archive) alone and see something moving the clothes on the rack. There was also a long hallway btween the theatre and the classrooms- there were many lockers there in the 60's- at one point along the hallway, I always felt watched, and I felt cold spots there on several occasions. Other people would run the hallway, even if they had no idea why... no one lingered in that hallway.
Anyway, none of this is really vengeful, but it might give some ideas for phantom haunting.

Hmm, great set-up.

Ok, a few poltergeist-y ideas:

- stage makeup either open or residue left on surfaces in the prep area or both
- she had a fright shortly before her death regarding an accidental stain that she had to get out (some clod with ink, perhaps). this isn't important except as a creepy perhaps symbolic visual: the current actress' dress is suddenly hit with a widening stain (like blood from a wound)
- does the ghost care about the living? if so, she may want to prevent harm to the current actors. maybe that's what all the scaring is about. so she might rearrange shoes, props, anything to stall the production during which she feels certain someone may yet again have an accident (this could be a really cool reversal on the reader, if it seems at first as if the ghost wants to hurt people, and breaks someone's leg, when in fact, she was pushing the actor away from one of those "danger" spots she remembers from her own life circumstances)
- I quite like the idea of food going bad for some reason. again death symbolism. so if students come to practice over lunch, perhaps they'll find their food has gone off even if packed this morning (with fresh ingredients! respond their incredulent moms and dads)

Sounds neat. Hope your story works out!

If anyone has an MP3 player, they could be sitting alone and listening, and hear someone whisper to them? So they think someone came back into the room, but they're alone still, and they go out of the theatre and play the song again and it's perfect.

^ Happened to me. CREEPY.

Also, if the girl had a boyfriend, maybe there is a certain boy with the same first/middle/last name, or who looks somewhat similar? I would generally use the names, since they're used less, but that's just me, and it may be I just don't see the other examples....but he would hear things, or things would happen to him more than anyone?

Although the ghosts that are there are not reported as vengeful, You might want to take a quick look at Le Petite Theatre de Vieux Carre in New Orleans. It is allegedly occupied by multiple ghosts.