Dear Mary: How do I cope with colleagues’ bad habits now I’m back in the office?

Q. I am placed in a social dilemma due to a proposed visit on the last weekend of June by an American friend who has been hospitable to me. She is great fun. However, it is also the weekend (planned far ahead) when I have staying a recent widow who has been even more hospitable, having had me to visit three times overseas at her seaside house, providing there delicious meals, tourist attractions and delightful company in the form of her other house guests. She is bringing to me a mutual friend, a charming elderly widower. She and he are taking me out to dinner on the Saturday night. But what do I do about the unexpected American? I don’t want to put them in the position of paying for her, too. I could offer to treat her but this will ruin their generous gesture to me and I feel sure they will refuse.