Re: recommendation needed
i think i'd have to agree with the strength training, but that seems to be an issue you can't overcome. if having weight forward is the issue, look at other bullpups.
FN's FS2000 is a great alternative to the PS90. it uses STANAG magazines (cheap, light, plentiful), fires a 5.56 nato (which is way easier to find than 5.7x28), can accept any optics that the ARs can (or your current optic) and it looks like something out of Judge Dredd!
another option in the bullpup line is an AUG. i've heard lots of negatives about the MSAR clone, but the Steyr is a great gun. however, it does NOT accept STANAG magazines to the best of my knowledge.
the M1 Carbine is an awesome and nostalgic gun. i'd avoid one with a paratrooper side-folding stock though, there's no such thing as a cheekweld on that wire stock. the solid wood stocked guns are nice, VERY low recoil (for quicker followup shots, not that she's recoil sensitive, you've already stated otherwise)
or, if AK's are an option, look for a bullpup AK. 47, 74, either one would be just fine.