If you have a facebook account, look for me on there and join the carseats for littles page. THose women know everything that there is to know about car seats.
The only thing I can figure is that maybe the straps in the back aren't laced correctly on the metal hook that secures the straps to the tightening belt...you know the part on the front between the knees that you pull to tighten and loosen them?
Good luck. HOpefully she's figured it out.
And a little carseat tidbit I just discovered:
The strap covers that don't come with the seats (like the cute animal ones you can get at walmart) void warranties on seats, can interfere with benefits from insurance companies in the case of a crash, cause the chest clip...that goes at armpit/nipple level...to be too low and can cause the straps to not work effectively!!! I had those on all our seats. I snatched them off in a heartbeat!
So, if you have them on the carseat you might want to take them off. Better safe than sorry, right? You can take a sock and cut the toes out and slide them over the straps if it rubs her neck. I did that with my seat:) Kinda ghetto but at least it's safe!! lol