Ahhh the ODD 3's! I swear 3 is worse than 2!
I've found that sticker charts work with children like this with a nice "carrot" to dangle at the end of it. (a special grab bag toy or lolly that goes home at the end of the day)
For example: They have to earn say, 10 stickers by the end of the week to pick something from the prize box. This will work for potty training too. First they get a sticker for going #1 on the potty and 2 stickers for doing #2.
Of course, they will all want to participate so you can base your sticker tallies on age of the child. Older children will need to earn more stickers since they are more "grown up".
Praise, praise, praise when she gets caught doing the right thing.
Patience - hopefully you'll turn her around.
Oops! Sorry - my post was in reply to the OP. Didn't realize this is an old thread.