Focus her, your and everyone else's attentions on her other (non-physical) interests and talents. Self-confidence is always a plus.
If she's busy with her artistic/ musical/ sporting/ chess etc. achievements, her looks are just another facet, and not a big deal.
Example :
8 yr old classmate : "We don't want you at our sleepover; you think you're better than everyone else just because you're pretty"...
DD: "No I don't. It's you who's always going on about it. It's boring. Anyway, I'm busy on Friday...my gymnastics club is training for X competition. I love it. Then we all go for pizza afterwards. Right laugh. Do you do any sports outside school? You're always really good at X in P.E...."
As her Mum, if/ when adults comment within her hearing:
OTT friend: Isn't she pretty? God, my girls would love to have her colouring. And those eyelashes...wow. She'll have QUEUES of boys outside in a few years..."
You: Yeah, she is a nice-looking kid. Mind you we're obviously a bit biased! Did you hear about how well her team are doing in the X competitions? She puts so much hard work into the training. She's made lovely friends there, too. They have a lot of fun together... How's your DD getting on with her X activity? I hear she's pretty good..."
Your DD then has it reinforced that good looks are nothing to be made to feel shy or guilty about, (which can lead to all sorts of other issues), but that it's not popular to boast about them, that it's only a small part of the all-round package, and that she has many more exciting things to talk about! And, crucially, to show interest in other people!