I've actually also been recently asking myself that same question. Just
this week I went out to go practice and I saw a beautiful girl
but she was with her mother. I haven't tried this out as
of yet but what I would do is I would first approach
the mother and say something like this
Me:- "Hi guys, sorry to bother you, I can only stay for a minute
...is this your daughter?"
Mother:- "Yes...why?"
Me:-"Oh great, well, I just walked past you guys and I
would totally kick myself the whole day if I didn't say
this but she looks amazing, her sense of fashion is
fantastic! Good job you've taught her well

"
(That would be an indirect compliment to the daughter
although I am screening it though the mother)
I'm going to try this out tomorrow but that would
just be my own general opinion of how something
like that would go down.