My guess would be that the seller has her listings set to file Unpaid Item cases automatically after 2 days.
This is the weekend, and the seller may be away from the computer, or if it is a business seller no one will be available until Monday.
If you do not hear anything by Monday, you might want to consider phoning the seller and sweetly explaining that you understood your previous agreement to mean she would send an adjusted invoice for the total after you had finished shopping.
To get the phone number, go to the right side of the Search bar and click the word Advanced.
Scroll down to Find contact information, click that, and enter the details.
The seller gets a notice that you have requested the information.
You don't say when the first Unpaid Item case was opened. Sellers can now open an UI case after only 2 days, - whether it is automatic or done manually. If no payment is received, the case is closed after a further 4 days and the buyer gets a strike.
So that's a total of 6 days.
How close are you to day 6? If it were me, I would call ebay and explain the situation. You have the emails where your seller reassured you that a combined invoice would be forthcoming upon notification of completion. Hence it is quite unfair to file UI cases when you requested the total as per your agreement.
Ebay may be able to halt the UI cases or at least will remove them if the cases result in UI strikes.
To contact ebay, at the top right of the page choose the Customer Support > Customer Support link.
Then click on the Contact eBay tab. Select a category, and you'll be given a passcode to use with the phone number but it expires so prepare to call when you're ready.
For now, though, if there is time, I'd say wait to see if you hear from your seller by Monday. You might,
but if not, you'll need to take some sort of action.
Paying full price for the items after being assured of a combined rate is unacceptable, worsened only by the thought of all those Unpaid cases.
Best of luck 
