My 4 year old was horrible to potty train. Rewards or songs never worked. I would have to make her sit on the potty every hour. When she would go potty I would praise her, which she loved. She was terrified to go #2, but one day she decided to do it and has completely used the potty ever since. My 2 year old just started potty training and will only use the seat that goes on the toilet. She loves to flush the toilet, but knows she can't unless she's able to potty. That has really helped with her.
Have you tried the potty song with her? Also rewards? I did both with my little girl and she loved it and was trained fast. For some kids you gotta make it fun because this stage freaks them out for some reason. With my sisters son he was so scared of potty.