She's relied on me for a decade. What do I do now?

It would be a shame to lose a friendship due to a third party but at least you would have tried to sort it amicably

This raises a point we have all ignored. Does Nellie enjoy this ladies company, view her as a friend and gain something back from the relationship, or is it a burden she has taken on and would love to drop?

If the first, then it definitely worth giving her a chance to explain. If the second, then do as some have suggested, a witnessed return of the key, but I do think a note of explanation should be included.

Swannys slow escape seriously runs the risk that she will never let you go. She will not ask whats wrong, she may guess but will be far too embarrassed to raise it, and would nott want to, and may well be extra nice to you to make up making it harder than ever to break the ties.

Think what you want the resolution to be, and work towards that.

If, after checking with the elderly neighbour, you ascertain that she was talking about you in this disparaging way, then you should clearly tell her that you are withdrawing your help.
As Ana and Anya have urged, return the key with a witness, end of story.

What a wonderful person you must be, Nelliemags. Hugs to you!

Nellie I am going against the flow here. First of all does your neighbour know by now you heard her conversation? If not I would put it down to her, at 91, speaking without thinking based on whatever the carer said to her.

Is she mobile in her own home? If so I would return her key and ring the doorbell next time you offer to help. Use whatever reason you want to gradually reduce your assistance, rather than cutting her off suddenly. If she is as clear headed as you say she will pick up on that and ask you if anything is wrong. You can then say calmly that you'd overheard that conversation and was hurt by what she said. It's then up to her to apologise and realise what she's in danger of losing. It would be a shame to lose a friendship due to a third party but at least you would have tried to sort it amicably.

I think that I would want to talk to her about the incident, and depending on her answers, take it from there. Saying what she did about your husband is pretty unforgivable.
Is she really grateful for your help I wonder?
20 years is a long time to be helpful to a neighbour, and as Mair says, make sure that she was talking about you on the phone ( sounds as if she was though).
If you are unhappy with her answers, then do as others suggest, and stop driving her around to appointments at the very least.
I came upon a similar situation to this some years ago, when I was in my thirties, we moved in next door to an old (mid sixties!) lady.On the other side lived a very nice
couple slightly younger than her.They seemed to do a lot for her, the husband did DIY
For her and helped out in her garden,the wife often took her shopping and to WI etc.
One day, having a coffee with her in my house, the 'old lady' confided to me that this couple were taking over her life and she thought them bored with each other, and helping her was one thing but she was getting fed up of them always popping round.
Well, I was amazed at this and thought how ungrateful some people really are, but it also made me think that you never really know how a neighbour regards you, on the one hand you think you are doing a good neighbourly thing, but maybe they don't think that at all and just take you for granted, or, in this case think that you really enjoy doing it!
I didn't say anything to the nice couple, although felt tempted to.

No matter what the carer said or didn't say there's no excuse for what was overheard, especially the remark about her husband. And she ought not to be discussing you in any terms with someone over the phone.

I feel sorry for both the old lady and Nelliemags , I still think I would hope to sort it out , but maybe not be such a willing message fetcher now that she has carers

I think you should check first before taking any drastic steps, as Jane10 and aggie said maybe the carer gave her a different version of events. You would think though that having known you a long time and been helped such a lot the lady would defend you.
As she has help now perhaps it's a good time to reduce or stop the help you give.

Yes, withdraw your help. Put the key in a bubble bag and post it back registered post or put it through her letterbox with a witness to that. No letter of explanation.

Take your own life back. She doesn't deserve you.

And make sure you give the key back with a witness.

My husband found himself in a similar position with an old couple who lived near us. He just quietly withdrew from helping them and it really was the best way. They had 3 daughters who lived nearby and were content to let someone else help their parents so we just told the old couple that some things were better dealt with by family.

I would withdraw my services, she has carers who are being paid to care for her why should you provide free duplicate care.

How horrible for you.
I would say, however, that my mum would say things about me that were quite spiteful towards the end of her life.
However, this lady isn't related, so I would withdraw from her if I were you.

Firstly are you absolutely 110% sure it was you she was talking about?
Do you know for sure she isnt losing her marbles? Do you know the carer hasn't told her a lie about you (for some reason known only to herself)?
The fairest thing would be to tell her the truth, in person, and see what she says and if there is an explanation other than her being an ungrateful old bag! However I can understand if you feel you don't want to. Did you speak to her yesterday or just slip away?

Keep away and let it go.

That was a shock for you ! Perhaps the carer didn't explain about the car properly and your Neighbour got the wrong end of the stick . If it was me I would try and calmly talk to her , sad to see an elderly woman getting it so wrong

Oh Nelliemags what a dilemma. I can quite understand that you might just want to have nothing more to do with her. Can you quietly and calmly sit down with her and discuss this? Ask if that's what she really thinks about you? Maybe she only heard the carers version of the story but that's no excuse for what else she said about you.
Otherwise -she has carers. Let them care for her! Good luck.