I can relate to this as the mom of a 3.5 year old who only JUST recently started using the toilet to pee (we are actually still working on the poop part, that is not going well!!). She had all the nice undies like yours, I knew she could do it, she would announce when she had to go and when she did pee, all the same things your daughter is doing. I found that it really wasn't helping to get into the power struggle thing with her, in fact, it was making it worse. Once I laid off a little she started using the toilet more and more, which led to her confidence rising, and here we are. For my daughter, it helped her to know that she was going to be starting gymnastics, and I told her all the other kids wouldn't be wearing a Pull Up. I really think this stuck in her mind and she made the decision to be a "big girl", finally! But I told myself that if she went to gymnastics in a Pull Up, so be it... I really had to let go a little. She was slow with most all the physical things she did, like crawling and walking, so it was no surprise to me that toilet training took so long.
It sounds like you are doing everything you possibly can! My advice is really to just keep doing that, but hang back a little and see what happens. Tell yourself that she WILL get it! She won't go to kindergarten in a Pull Up or diaper! People used to say that to me and I would roll my eyes, but it's true. Now if I could just get my little girl to try #2 in the toilet - I might be posting my own question soon!! Good luck and hang in there.