Best thing to do? Keep the screenshot and screenshot the boy's message, save it into a folder, write down date and what occurred and then, ignore. Best if your dd does not message the boy back.
If he asks why his message is blue ticked and she is not replying, still don't reply. If he asks her in person, she can say my parents don't allow it.
Ignore, ignore, ignore. Maybe your dd has been unintentionally mean, maybe not.
Just ignore otherwise you become the Drama Lama.
mean, causes drama and is selfish
Is not exactly offensive. It's childish and children act childishly. If you complain about such a minor thing you won't be taken seriously if anything serious happens as you and your dd will be seen as the sensitive ones. Your dd has to learn to play the game.
Instead, build her confidence, what is she good at? Where has she got friends? Netball team? Any other clubs where she is with people who like her?
Kids have to learn to navigate this sort of thing unless it becomes threatening or hideous lies are spread of course. Don't fight all your dd's fights, let her learn to shrug some stuff off, assert herself and sometimes try and get on even with the popular girls who will sometimes also be mean and petty.
It's playground games, don't enter this space as an adult with your adult spectacles on unless absolutely necessary. Coach your dd and help her grow a teflon coat. This will help her in her future.