Hello M.,
Only you can decide if your child is safe with her dad, and if you know she is, than I would continue to send her there.
I have a four year old son who acts the same way. He has been going to preschool since he was 21/2 and he still cries 2 years later. We are very close, I am a stay at home mom, so he is very attatched to me. Every time I leave him at school, I have to stand there while his teacher peels him off of me and he is screaming and crying. Walking away is the most difficult thing I have to do. His teacher tells me that he stops within 30 seconds of me leaving the driveway. It is so upsetting and stressful. I know he is safe when he is there, I know he just wants to be with me. So, I continue to bring him and tell him that he has to go to school. Kindergarten is coming and he has to be prepared. The time your daughter has with her dad is important, and all I can say is that one day they will grow out of it. My daughter cried everytime I left her until she was in the 2nd grade. Just realize that your child loves you and wants to be with you. Take the crying as a compliment and realize that walking away means helping them learn how to cope with a sometimes difficult world.
I hope you find some comfort, and if you receive any help that works, please pass it on!
sincerely,
A. L