@ladylovesmilktray YANBU, and it's not rude or ageist for you to complain about this entitled woman. You are simply stating that she is of the older generation. As a few people have said, the elderly are not ALL like this, but you can bet the ones who are, have always been like the same, and have always had people wait on them hand and foot. (And have always complained about everything people do for them.) I think we all know someone like this.
To be honest, I have heard a lot of stories like this, where people are volunteering to get stuff for people and they are run ragged doing it.
The more I hear about it, the more glad I am me and DH never volunteered. (I have my own family to look after.) If I were you OP, I would tell whoever is organising this, that you no longer wish to go to this woman's house. OR just stop doing it. You do have that right.
Also, it comes as no surprise to me that one woman took the piss out of someone, then dropped it out that her adult daughter visited the previous day. Me and DH know a woman (divorcee) who he used to work with, who is 15-16 years older than us (retired now,) and she has 2 adult children who've left home, who never do anything for her and rarely visit her.
One lives 30 miles or so from her and the other one lives 10 miles away. We live 40 miles away from her. They rarely visit her but she never visits them. (It works both ways IMO. She is in good health and has no reason to not visit.)
So she always used to contact DH to ask him (and me) to do this and do that and fetch this and fetch that and asked if we could help her move house etc... DH was a fucking mug and did it every time. (AND asked me sometimes!) She NEVER contacted him or me unless she wanted something.
Last year, DH had quite a dangerous operation, and was laid up for 2 months. She never ONCE rang to see if he was OK, and only rang (3 months after his op,) when she wanted taking to a hospital 40 miles from her (so 70 miles from US,) for a routine appointment. I was fuming when he said 'yeah me and chicken will take you.' DH used to ring her every other week to say hi and make sure she was OK, and she never rang (unless she wanted something!)
After this (Mid November it was we took her,) I put my foot down and said we are NOT contacting her again, as I am pissed off that she never gets in touch unless she wants something.
So anyway, fast forward to mid February this year, and we had heard NOTHING from her. Then when the rumour came that lockdown was coming because of coronavirus, she fucking rang (the Friday before) and left a message saying 'are you two coming to visit me soon? I could do with some supplies when you do. Let me know when you're coming and I will give you a list.' Cheeky cah. 
DH didn't ring back as he was feeling a bit rough that weekend with a migraine, and a tummy bug, and then we went into lockdown. He rang her back first day of lockdown to say we can't do much, and hadn't rang her back a few days back as he was quite ill. But she never answered so he left an answerphone message.
9 days later, no call back from her. Hopefully one of her 2 adult children can help her. 
Frankly I hope we never hear from the ungrateful, entitled woman again!