T.B.
Hi K.,
I don't have any advice on what to do as my daughter is in the same boat... so at least you can know that you are not alone. My daughter will be 3 in February as well. She has shown interest off and on, has used it successfully and then has no interest. We've done EVERYTHING you have and I also have an 8 month old and have tried the whole "babies where diapers and you're a big girl now" and she will say no she's a baby and wants her diaper. It comes in phases. She'll then all of a sudden want to use the potty. We tried putting her in "big girl underwear" for a weekend and put her on the potty every 10 minutes. It never failed that as soon as she got off the potty, she'd go on the floor. It got so messy and she didn't seem to care, so we gave up.
The one bit of advice I have consistently gotten (including from her doctor) is to not push it. All kids potty train at their own speed and it's one of the few things they can control on their own, so let them be their own guide. My mom said I was "late for a girl" and was potty trained around 3 or just after. I really wanted to go to preschool but had to be potty trained and I guess that was it. So I'm hoping it will happen with my daughter too. Don't worry... she's not going to be in diapers forever. It'll happen when she's ready. My daughter is stubborn and the more I force it, the more she seems to resist just because she can.
Good luck and try to take a step back for a little while and see what happens.