Just thought of this. In the vanilla game there are some high value rings and enchanted stuff ranging upward of 20,000, and there are mod items of very high value - have one at 90,000. Go to some poor merchant with say 500 septims and sell the item and by it back at full value. An hour or two of that would eat a hole in your stash. Just did it at the Feed Bag and it works.
This is true but it would sit uncomfortably as there is no logical reason why this would happen...
You're on PC. Why not simply install http://oblivion.nexusmods.com/mods/25078, whose stated purpose is:
"Completely overhauls Oblivion's economic game to make it immersive and interesting, and optionally making it harder to get rich fast."
-Decrepit-
A good point and it's possible that Cyrodiil's merchant may well become rather - shall we say - less generous...
I suspect though that I shall simply tell her that if she doesn't want it, she should drop it, but maybe stash somewhere so that if she ever were to actually need it, then she would have it secreted away...