27 months old and still hasn't even peed in the potty?

My daughter is so smart in every other way, she just refuses to pee in the potty. I have been trying to potty train her since she turned 2 and she just will not cooperate. I always try to make it fun and be all smiles and very encouraging but every time I sit her on the potty, she jumps off and runs away. This morning she woke up with a dry diaper so I knew she was going to pee and even at the mention of the word potty, she started screaming hysterically until she turned purple in the face! I put her on the potty and she just screamed like I was trying to kill her and ran off naked down the hall. She kept screaming "Diaper!" the whole time. I know she is ready to be potty trained, she always announces when she has to pee or poo but as soon as I set her on the potty, all hell breaks loose! I always tell her she is a big girl now and how proud I would be if she pees in the potty. I try to keep a positive attitude but this is wearing me out. 27 months is too old to be not even be trying. As soon as I put her diaper back on this morning, she peed! Ugh, this is frustrating! I ordered her the book "Once Upon a Potty" but it hasn't arrived yet and I am wondering if it will help because she seems dead set on not using the potty. Will she be is diapers forever? It's kind of embarring to have her still in diapers at this age. Is there anything I haven't tried? Please help!