my advice is to

1. guide her to walk down different street to avoid them.
2. reenforce to her that she did nothing wrong, and 3 remind her of societal dangers of females dealing with groups of dudes.
   they're like angry apes. with guns and patience. we can argue about equality and women's rights and all that but bottom line is a young female is, unfortunately, a vulnerable target in certain scenarios. she has to be aware of her risk vectors to react better.

Not practical, but take their picture, look them up on social media and expose them to their family, workplace, and friends.

Shun the men in your life who behave like this. Don't watch media that shows it as romantic or funny.

And yeah, if it's safe, yell at the men.

(Eta: this is directed to the adults, not the child)

Tell her to say "I'm 13 you pervert. I guess women your own age won't have anything to do with you".

Unfortunately I don't think there's anything the child or the parent could do in this situation that doesn't risk escalation to something violent.

The real solution is for society as a whole to stop tolerating this shit behaviour and call it out when they see it. "You're wolf-whistling at a kid, Dave. Are you in the fucking Epstein files or something?"