I don't think there's any harm. If my daughter looks lovely, I tell her so, just as I would praise her in any other area - for example, for good behaviour or doing something well at school.
This. As long as she is getting praise for other important things then I don't see the problem.
I'd hate for my daughter to grow up thinking she was ugly because mummy never told her how pretty she was, in the same way I'd hate for her to think she was stupid because noone ever said how clever she is