I'm no expert in this area at all, so please bear that in mind. I don't know how to directly reset her inventory, but we may be able to do it indirectly. What you might try (after saving first of course) is using the command console to kill her. Then resurrect her using simply the resurrect command without a 1 or anything. That should respawn her with her original stuff as far as I know. I have used kill and resurrect commands before, but not exactly to reset a merchant's inventory. I recommend you read this reference and see if you come to the same conclusions I did:
http://www.uesp.net/wiki/Oblivion:Console_Command_Tutorial#Resurrect_and_Kill
Good luck. :foodndrink: