People with this disorder are compelled to steal things, generally things of little or no value, such as pens, paper clips, small toys, chestnuts, or packets of sugar etc.People with this disorder are likely to have a comorbid condition, specifically paranoid, schizoid or borderline personality disorder.Have you ever wonder why there are people like them? the answer in one of the psychology books, that these people who stole things without even value is desperately seeking love at home.Till here everything is alright from the medical window.But your case is not fitting this circle and I am excatly thinking as tess_916 said above.Your missing or lost things are valuable stuffs or just RANDOMLY lost items?This is the big clue which tells you that if she is really sick or a thief.

_________________________________________________
All human beings are born free and equal in dignity and rights.They are endowed with reason and conscience and should act towards one another in a spirit of brotherhood.