Messaged buyer to wait for combined invoice, buyer paid individually, didn't read email properly.

[dmh160161]

Yesterday I sold 4 items to a buyer, when she was bidding I messaged her and asked her to wait for a combined invoice at end of all auctions and I would be able to post all items together for cheaper in a 3kg bag, she was very happy with that and messaged back saying thank you. The last item ended last night, yet she made the payment for all items paid individually, didn't wait for invoice.  

I now can't print out a 3kg label now as only coming up with one 500g bag, and 4 items won't fit anyway, and I have been charged 4 individual postage fees as well.  I have messaged her but not sure what to do.  Do I refund her money and start again (not sure how this effects fees and protections) or just buy a bag at post office and refund the difference in postage less charges.  I always use the eBay post bags so have them in stock.  I was hoping not to have to go post office as I go overseas on Friday morning. 

Really happy I have sold items but this has made it complicated now.  If only buyer had just waited, I would have had her items posted this arvo.  Can anyone give me some advise.