O.P. here.
Thanks for the replies, everyone. My etiquette question was whether or not it was rude to cancel an offer that was not intended to be open-ended but was taken to be so.
A comparable situation would be if Hazel complained about not having money to pay her bills, and she gladly accepted an offer to write her a check, but then said, “Oh, don’t write it now because I can’t get to the bank this week”. Then the following week she called and said the same thing, and then did it again the week after that and the week after that. Obviously she expects to get the check in the future when it’s convenient for her. But meanwhile, I’m realizing that she has close relatives who could help her out, and I’m realizing that giving her the money would be a bigger sacrifice for me than I originally thought and that I feel like I have to keep the money available until she decides she wants it.
I’ll probably hear from Hazel tomorrow, and I’m going to bring the matter up and let her know that the offer is no longer on the table.
It hadn’t occurred to me that Hazel would need permission to take the grandkids. That may be the real reason behind the dawdling, but she doesn’t want to say so.