If she doesn't ship, it wouldn't be NPS but INR that you'd file. But give it a bit of time. Remember you have 45 days to file a dispute so time isn't of the essence at this point.
ETA: As for miscalculating the shipping price, it really isn't your problem and she can't make you pay. The fact that you offered is nice but unnecessary and hopefully, she'll proofread her listings before posting them next time.
A buyer pays for her item promptly in this case... She has no communication
so far from the seller with regard to shipping her item..
Seller has a certain amount of time to ship ( 4 days or 7 days is this correct?)
Why should a buyer wait 45 days to file an INR or 45 days to wait to
get their money back?? Just on principle alone with no communication I
would not want to wait any more that I had to
If the buyer can't file a NPS (does ebay still allow a buyer to file
a non performing seller charge/complaint?)
I would wait a reasonable amount of time & then I would file an INR
& for me that would be 2 weeks...if this is an international transaction
then perhaps a little longer but certainly not 45 days..
Under these circumstances & with the seller's feedback, I would
light a fire under the seller's butt to get some acknowledgement here...
But that's just me...
The extra shipping was a courtesy from the buyer which she did not
have to do.. The seller should assume responsibility for her miscalculation..