Yes, you can export inventory from one account and then import import it to another store. However you will have to edit the spreadsheet once you export it before you import it to the other store because some of the data will not work from one store to the other.
To export your inventory items go to your online Dashboard / Items - On the right side top corner Click "Actions" botton. Then select Export Library. Either format works.
I would export your inventory from both locations.
Now open your exported spreadsheet(s) in you favorite program, Excel, Google Sheets, Apple Numbers.
Move the data from one spread sheet to the other. For new items copy these Columns - Item Name, Description, Category, Sku, Variation, Price. Now the Current Quantity column you want to paste it into the correct Column of the other store. If you have more than one location make sure it is pasted into the correct location. You will want to add it to the New Quantity Column so it adds it.
Note Don't Copy the Token as they are unique to your store and will be auto assigned for new items.
To update items that are currently in both stores you are just going to have to edit the New Quantity column in the spreedsheet by finding the item in the list. If you sort both of them by item name it may make it easier.
I would also put all of her items in the same Category, This way you can pull a Category report and see what you sold of hers. It will be hard to figure any Credit card fees.
Once you are done editing the spreadsheet you can upload it by going back to Item - Click the Action Button and Import Library. Make sure you select modify...
