Ebay fees are calculated on the final selling price. So you will still be paying ebay fees made up of listing fee plus final selling fee.
I think its about 10%. Paypal charges differently as there is a fixed fee per transaction then a smaller % on top. Again the schedule of charges will be somewhere in the paypal website.
I have bought and sold plenty on ebay and have never had a buyer dispute the fees part, people usually pick up because it saves the postage.
I often search for items purely on 'nearest first' to find things I can pick up, and I've never quibbled over the fees.
I think she is trying it on. The TOTAL ebay and paypal fees for that item might be in the regionn of £20, but you will still have to pay the ebay fees. Find out exactly what the portion is, then if you feel like it you can offer that reduction to her.
Or, you can say 'no I want paypal and I will post it to you' (I've had that done to me by someone who had to drive past my house to get to the bloody post office!!!).
Or you can tell her that this should have been requested before she bid and that the answer is no.
At worst case you can open a paypal dispute and get the transaction cancelled.
And be warned, if she pays cash and takes the item away,a cheeky mare like that could then turn round and open a paypal dispute claiming that she has not had the item! If she has checked your feedback and can see that you are new to it, I'd be very suspicious that she is trying it on.
I'd take paypal and send the thing recorded delivery. But don't reply today until you have all your figures and decided what to do.