Nah he wont be able to know whether she's a virgin or not but its better to say the truth instead of lie and cheat
its nt her fault its forgivable
To tell or not to tell depends on cultural back ground. In some she will be totally rejected and her life will be a lonely life. So it is pragmatic to speak a little lie and dedicate herself to her husband completely.
In the first night her husband will not be able to know that her wife is used to intercourse unless he shows her to a doctor. Nobody goes to a doctor for such purpose before marriage or immidiately after marriage.
She needs to be completely honest with her fiance. She owes this to him. If he truly loves her he will understand. it is not her fault her dad is a rapist. If he doesn't understand and is not supportive towards her then it wasn't meant to be. She shouldn't be living with anxiety over this. The right man will stand by her side.