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Unfortunately they can do what they want in this regard. It may be discrimination, but it's not illegal discrimination.
However, perhaps there is something about your daughter that makes them hesitant, particularly if other family members have worked there. Consider honestly whether maybe your daughter is not quite mature enough for a medical practice.
They may also see your daughter in a different light because you are the manager. But, I'm wondering - to whom do you report? A Board? So if there's someone to say no, you're not really in charge --unless you have a contract that says you are.
It could be time to assert yourself and your management abilities. Or it may be time to move on.
Only you know for sure.