Combined postage nightmare; am I correct?

[Diege]

Sold two tops to an American buyer using BIN. They were from 2 separate auctions and she paid for postage for each before I had a chance to combine postage. I noticed this and e-mailed her offering to send a small refund if the tops cost more to send than she had paid for. The postage she sent came to £8.98 and to my surprise when I sent the parcel it cost £11.11p to send . I explained that under the circumstances I wouldn't be able to offer a refund and that it's my error so obviously not expecting her to pay any more.
As a buyer I'd think no more (would be secretly pleased and a bit guilty), but would she be correct to still request a discount based on my earlier offer to combine? Or is my sleep-deprived fuddled brain going into overdrive on this??

[ADragonIs4LifeNotJustHalloween]

"offering to send a small refund if the tops cost more to send than she had paid for"

They didn't, thus you don't have to offer a refund.

[Diege]

Yes you're right . I've just checked the wording of the message I sent and I did indeed relate any possible refund to the price it would cost to send. Clearly a combination of new baby brain and recent bad buyer experiences! . Many thanks for sorting me out