Well the gap is supposed to be there. The pulling on her shoulders may be how she is adjusting the straps. First thing to try: make sure the hip belt is tight enough. Then losen shoulder straps until the pack rest more on her hips. Let us know if that helps at all. It you can, send a picture including the hip belt placement as it will be easier to see what is going on.
The jam needs to be packed right, IMHO, in order to get the most out of it since its frame, if you want to call it that, is very wimpy. What sleeping pad is she using and how is it packed? The ideal kind of pad, also in my personal opinion is something like a ridge-rest (vest) or a zrest (next best) you should try to uses it if possible to support the pack as an extra "frame".