Dear Mary: how do we deal with a neighbour who is stealing our friends?

Q. A dear friend of long-standing has a propensity to make friends of our friends — people she has first met in our house. She invites them to hers, some even to her principal abode nearly 650 miles distant, but doesn’t include us. Some have then invited her without us, some have even taken holidays with her. I don’t think we are paranoid, and perhaps we really aren’t that interesting, but still it’s not terribly pleasant, especially since some of these old friends, having been siphoned off by our neighbour, now have less time for us. Sometimes we vow we will not introduce her to any new friends but this seems rather petty — especially as we enjoy hosting small dinners and our friend is very convivial. We are sure she has no idea of the havoc she is wreaking on our feelings.
— X and Y, Saône-et-Loire

A. Give a small dinner to which you invite your convivial neighbour, one of the siphoned friends — and a garrulous plant.