how many return requests can a buyer make?

[shell442007*07]

I recently sold a ring on auction to a buyer who messaged that she was very happy and excited to have won the auction.  A couple more messages in the same vein then a message that she was very worried and concerned that the gemstone may not be genuine, did I have a certificate of authentication and how much did I pay for it and where was it bought.  I told her where I bought it, could not remember how much I paid and did not have a certificate of authentication but trusted the company I bought from 100%.  I also said that if the jeweller (she was going to have it remodeled) thought it was fake to send me his report and I would happily refund her money.  This was all before she even received the ring.  As soon as she received the ring she put in a 'Return Request' with Ebay saying it didn't seem authentic, had scratches (it was listed as pre-used) and was made in China, she would never have bought it if I had said it was made in China.  I immediately accepted the Return Request and messaged that I would fully refund her.  She said she would return it the next day.  After a couple of days I messaged to ask for tracking details and she replied that she had taken it to one jeweller who could not authenticate it for her and had taken it to a second jeweller who thought it was genuine but was very busy and would I mind waiting until she could take it back to him.  I said I would mind and why was she taking it to jewellers when she had lodged a Return Request and I knew it was genuine and she didn't need to know as she was returning it.  Now she has closed the Return Request and sent me messages of apology but I really don't think I have heard the last of her.  How many Return Requests can she lodge?  Sorry this is so long-winded but didn't want to miss out anything that may be relevant.