Hi B.,
I know that you are frustrated and discouraged. These can be tying times! Of course, as you are teaching them to drive a car, you look back on these times and laugh, wishing they were 2 once again.
Your daughter has learned the "ropes" of getting the comfort that she desires to do her business. I know 4 year olds that use this trick also.
I am a prechool teacher of Older 2's and Mixed 3's. I have also raised 4 children myself.
The main train of thought is to ALWAYS keep in mind that you are the adult, the mom, here. She is 2. She will do her best to break you down to achieve her means (the diaper).
I also do not recommend that parents sit for long periods of time with them while on the potty. That becomes a captive audience for attention. The bathroom is a room where we do our business then move on to other fun things. I never ask the children if they need to go. I tell them that it is their turn to go. They don't take toys in there with them but I have a special place for them to set them so no one else will get them while they are in the bathroom. No books are allowed, but I have walls of interesting posters to view and they are changed often.
I am just saying, change your approach. If you have to tell her the diapers are all gone by a certain date on the calendar, etc. She will soon get with the program.
If your child is a young 2, with a birthday after Janaury, you might want to wait until they are 30 mos. or so.
My rule of thumb is that if you can talk to me about the bathroom procedure, then you understand and recognize your need to use the facility. If she doesn't recognize the urges, she isn't ready. It sounds like she does, though, wanting to take off her wet diaper, etc.
These are frustrating times.Hang in there and remember who is mom in the house. What she says is the rule of the house!
Good luck!
Cathy