Should someone visit a bird they sold?

We bought a atiel from someone in December. Paid $60 for the bird and cage. The bird has been doing very well here, bonded with us the first day we got her. The owner asked that I remain in contact and let her know how Casper was on occasion because she cared a lot for her. I agreed upon occasional emails. The owner admitted to me that Casper didn't have much to do with her, only her husband. Well now she is asking me if they can visit Casper! I think this is a little much to ask. We did pay money for the bird. During the emails over the past month the girl has offered to "birdsit" and everything. She keeps telling me how much she misses her and such. Told me if it didn't work out she'd like to have her back, etc. We told her before we bought Casper that we would not feel comfortable having strangers come visit Casper, but I had no objection to emails. What is everyone's opinion? What is the best way to handle this?