Yeah its a pretty well established fact that stock front and rear sights on Glocks are the "weak link" on the guns...all of mine get replaced as soon as I get one
But again...you said erratic....If the sight is off...then it would always be off in theory
I still say there's more going on...Unless sight is moving around each time it gets holstered/unholstered on a draw
Where's our resident firearms training instructor when you need him....
Ill agree with that, I replace all my Glock sights the second I bring a new one home. Even with factory sights I highly doubt that it is her problem. Of course they get loose but it sits in a recessed groove so it cant shift left or right unless it lifts up out of the slot, and if that happened she would definately notice it.
If her rear sight was not aligned correctly her groups would not be effected, it would just be the location of the groups that were off.
Unless it is a VERY used and abused gun with a VERY high round count I doubt it is the gun. I have a G17 that has been through hell and back and has over 25k rounds through it (was given to me by a family friend who used it for competition shooting) and I can still put up nice groups on the paper. Why don't you shoot it for her and see if it groups fine in your hands? Or either let her shoot another Glock and see if the groups look the same way.
It definately sounds like a user problem, not a gun problem. I know some guys who have been shooting for longer than I have been alive (I'm 21) and still can't shoot worth a crap, technique is very important and even a little minor flinching, eyes closing, etc. can have a huge effect on her groups.