sorry to vent, customer trying to rip me off! Options

[Dead Air]

I do paint, wallpaper, drywall finish, small contracting jobs like bathrooms and kitchens, decks, etc.
A former customer refers me to her sister who bought a HUD house and wants me to do a couple tile tub surrounds, float plaster on the bathroom walls, tape some cracks, and generally prep for paint.
Some of the work is flat rate, some hourly.
I giver her an estimate, in writing saying I need some money down and will ask for "progress payments" as necessary.
When she realizes her family is not going to help like they said they would, she hires me to:
Paint the kitchen
paint the bathroom
wainscote the kitchen
paint the apartment
install bathroom sink with new fixtures
paint the kitchen cabinets
turn on the water
Install kitchen counter
install tile back splash over new kitchen counter

I tracked my hours to the minute and every receipt for materials.

The whole job cost, maybe, $3200. Not Much!
I go to collect a progress payment,
Customer says "I need an Invoice"
I photocopy all receipts, do an invoice word perfect and customer says I OWE HER MONEY!
(MY girl friend is a CPA, she checked my numbers!)
I demand payment for materials...She cans me off the job...I want the $500 balance, she says come get your stuff out of the apt. and I'll give you $200....I go to get my tools and ask for a check and the asshole says, I'll mail it to you, I say when and she says when you get it!
I was freaking out.
In the mean time, she changes the lock on the door and has her 250 pound kid come over for muscle.
Freakin' (IMG:http://www.914world.com/bbs2/html/emoticons/barf.gif) Bullshit!!