[audibell]

Don't pick up your gear until after the gig, you made a committment and you can see this through. I've had this same situation where the "talent" failed to do a couple of things herself, and blamed everything that went wrong on me, including the air conditioning, her nervous and almost mute children and the too loud jazz combo in a 4 second reverb cathedral; oh, did I mention waiting an hour outside until the verger came and unlocked the space 30 minutes before show time?

So, firstly understand that these friends cease to be friends when they hire you to do anything, so customers are always right until they bitch unreasonably.
You assumed too much by relying on what she said she had which she believed to be adequate - never assume the client's gear works or even exists - she told you what she needed which your first visit - good move - would have confirmed. Resist all protests to use the client's gear unless it's worth more than a Porsche - be independent always, even if you have to leave most of it in the car under blankets.

You have to tap these harrassed director-types gently on the arm and tell them you need five minutes to set levels and take the brightest-looking kid and have 'em scratch each mic basket; the kids love it and the teachers focus on what they forgot to bring instead of you. Use duct tape to secure cables on the floor or the grandmothers will trip and sue you - ie you'll never work in this town again - also tape the power cords to the wall sockets and you may as well discourage curious fingers playing with the karaoke by taping the various cables so they can't be yanked out except by you. I even tape the mic stands to the floor 'cause twelve year olds love to trip on anything. Beg, borrow another tape/CD player on the assumption that her's won't work on Saturday - you'll be a hero as quickly as you were a bastard -

Have a back-up for everything, even if you lose money on this one - the experience is priceless even if painful.

Make sure you have contact info on little bits of paper for all the kiddies whose parents will want to hear the recording you're going to make of this gig - they'll gladly pay 10 bucks to hear little Suzie warbling into your Tascam 2-track cassette or better. You might as well make something from this angst-session. Don't worry, your friendship won't be over if it's not perfect, nothing ever is and the relief she'll feel once it's all over will calm the troubled waters - but don't bail on her now or be uncooperative, even though your feelings have been well smacked - she's under loads of pressure - maybe even her job if she's a teacher.

Make sure you can get a clean signal on everything and record it to prove to her later; maybe the mud is ac and reverb in the room though it's probably too much PA gain, turn it lower than she wants and turn a speaker to reflect some sound towards the kids.
Try and have fun.
WT