She was questioned about what, and then what happened?
HK immigration knows when you leave HK. If you were not allowed to leave they should have stopped you.
You’re assuming left hand knows what right hand is doing all the time.
Because of rule change Immigration Department might not have enforced new rules, even if CHP wanted it to.
Ideally mere presentation of a person under yellow code at the border should automatically discharge the quarantine order placed on that person. But HK Govt isn’t that efficient - or common sense - for that to be the case.