Really,you sumed it up yourself.If she was terminal or something,they would no doubt be at the hospital alot.
I think its what actually got her in the hospital that may be so upsetting or personal.She may have had a breakdown,suicide attempt or something not loudly mentioned usually.
If this is really bothering you,you might need to very 'seriously' ask your girlfiend if her mother is living or dying and let her know how deeply this is effecting you...
oh yeah,check your PM's axl.
Try once,fail twice...