If the flight was full-ish, she would have had a problem finding a vacant seat. Likely a flight attendant would then ask “where are your parents” and then loudly “has anyone lost a kid?” in four languages (easyjet Suisse from those gates DZ not U2).
If she had found a vacant seat adjacent to another kid, she might have got away with it.
Apparently they have already closed her route with a slab of plexiglass.