I'm on the side of the lady passenger on this, I'm afraid.
a) No doubt she would have placed her bag in the locker above her seat had she been able.
b) I don't care who you think you are, you don't take it upon yourself to interfere with another passenger's belongings in order to convenience yourself.
If the lady was an off duty crew, most likely was an "op up" ...if so, both she and the crew on duty were wrong.
I still think the active crew member should have been more emphtetic and handled the situation with some finesse, rather than give the pax what he got !