They’re not fleas, they’re “sand flies”. There’s plenty of medical info out there on the internet on how to treat it but your friend’s is the most serious I have ever heard about........
They are crustaceans , tiny crustaceans. And when I read about them online they are always in the feet. But she thought, being a California girl, that she could lie on a towel in the sand. We don’t have those things here. So she got them in her spine and they are all inside her now, internally. It’s really bad. She has muscles she can’t move, but apparently it isn’t lockjaw.