I am actually going to guess that what stops the process when LW is present is that LW's daughter in law is from a culture that eats differently than LW prefers and LW refuses to eat what the family usually eats so it's just easier and less confrontation to allow LW to take over the food for the weekend. Either that or the daughter's family likes to eat at significally different times than LW prefers, but my money's on the "a single shake of any spice jar in the food means that lo, your foreign food is too spicy for me" thing.

I know fox guessed unexamined homophobia, but my money is on racism that was carefully excised from the letter because the LW knows how bad it would make them look.

(EDIT: Also, the answer I would have given, in addition to Carolyn's short and pointed calibration check: "It sounds as though the frequency of your visits may be overwhelming. Even a much-beloved relative [subtext: ie Not You] visiting can disrupt a household routine and eat into time needed to keep ahead of the chores -- and that's during normal life, not pandemic life. I advise cutting back the frequency of your in-person visits, switching to frequent Zoom calls to keep in touch, and offering your daughter the money you're saving on gas for no-strings-attached household help." But from the between-the-lines reading, that money would have a lot of strings attached to it, and I would NOT be surprised if the daughter said no.)