@Alsace Gal
In one of your post responses, you mentioned that not only does she have a car but that she is also a Uber driver.
Ask her how much a ride to Costco would be. Then multiply it by 4 ( two to go and two to return ) and ADD that to what she owes you.
The fact that she helped you lift things without being asked after your sister passed, does not give her the right to abuse your kindness.
We teach others how to treat us by our behaviors. She needs a refresher course. My words to her: until you reimburse me in cash for the two Costco shopping trips, I am unavailable to provide chauffeur service.
Isn't there curbside pickup service at Costco or even home delivery ? She'll probably need a membership card for this....hers !
( If in the future after reimbursable, I will wait in the car while you handle your Costco errands. )
We make a living by what we get. We make a life by what we give.
Sir Winston Churchill