My advice would be to set your daughter(and son) up for counseling. She can talk to the counselor about her expectations of her father, develop a plan and have a safety net in place when and if the father does reject her.
If the father doesn't reject her, she should still have access to the counselor because the father may not be what she's envisioned and if he's actually causing emotional stress for your son, he may very well do the same for your daughter.
Once her feelings are validated through working with the counselor and she hears an unobjective third party's views on the situation, she may not want to pursue the relationship at this time. Or she may want to have a sounding board for the newly formed relationship.
I'd reccomend a counselor who has experience in this area.