Hi, Jennifer. Well, Sweetie, I hate to say it, but what your daughter is doing is actually normal for her age. Testing is absolutely right -- she's coming into a sense of her personal power, physically and in her relationships, and she's experimenting with it. She's probably not verbal enough for your "bribes" to mean anything to her. The promise of a reward after she sits still for 5 minutes doesn't mean anything to her, because she's getting all the reward she wants by rolling over, asserting her independence, etc., while you're trying to get her to do something she doesn't want to do.
I had the same problem with my son when he was nearing 2, also. Once babies get mobile and become toddlers, they are a force of nature and very hard to stop. It's not natural for them to sit still. I learned to dress my son one limb at a time, to sort of sneak him into his clothes, etc., but you're right -- a messy diaper is something you don't want splattered around the room.
Here's what I think might ease the problem a little bit, anyway. Your daughter sounds just HUNGRY for mastery, for independence, for being able to exert herself and assert herself. I would try giving her lots of opportunities to show what a big girl she is, how well she can do things all by herself, and then maybe she will not need to show herself off by fighting you all the time with changing and dressing. Try making sure that she has space to run around most of the time without being restricted or scolded. This will give her some safe independence without getting her in trouble with you or getting on your last nerve.
Give her toys that she can use to show mastery -- they used to have a doll with zippers, snaps and buttons which kids could use to learn zipping and buttoning. Let her dress her dolls; teach her to put on some of her own clothing. Maybe she could put her shoes on, and then you can tie them. Maybe this is a good time to introduce her to taking turns; make a game out of it. She's not going to be very good at it just yet, but I get the feeling these are the kinds of things she wants.
Plastic building blocks, like giant Leggos and stuff, may be good for her, too. Show her how to build things with them. It sounds like she may be precocious, which means a bit ahead of her time in some things.
Remember that she's exploring and trying to figure everything out. Kids this age LOVE the new concept of cause and effect. She knows she can get certain reactions out of you when she does certain things. Toddlers are often drama queens when it comes to attention -- it's not a bad thing, but they like big reactions, and they may do anything they can to get them. Try giving her big reactions and lots of praise for other things, and minimize your responses to her squirming around for bathing and dressing. You will probably find that she will do more of the things that get her the most attention, and will not do the things that do not get her a big reaction quite as much.
They like rewards, in other words, and the rewards have to be IMMEDIATE, because they simply do not understand delayed reactions. The only reality for a toddler is what is happenning RIGHT NOW.
Well, I hope this is helpful and that your little girl truly does become the happiest toddler on the block.
Peace,
Syl