There are a couple of points worth mentioning here.
The first is that technically f/a's are not supposed to leave their door during boarding.The number of cabin crew have been reduced over the last few years and if something happens how could you possibly get back to your door to carry out an evacuation?
The service department have a different idea of what is important to what our primary role really is.
The second thing is that if someone is that short that they cannot reach the overhead lockers why didn't they ask for help?
Doesn't take much to politely ask someone especially if they have flown before and know that they will have difficulty reaching the locker.
The lady in question must be very short because how do the f/a's on some of the Asian carriers manage?