Just to clarify, as many seem to have missed what her response was....
I noticed the error and mentioned to her what has happened and why, also apologising.
Here is the conversation. I remember them both as personally i noticed she didn’t appear like it was new news.
Boffin: I am so sorry X, I have confused the gardeners payment with yours. Underpaid them and overpaid you.
Cleaner: Laughter, I’m not doing your garden for you too.
Boffin: What would you like me to do, leave next weeks payment or take a small amount off the coming weeks?
Cleaner: Just leave it off next week. I do enough for you, I’m not doing your gardening too.
Boffin: Would you not prefer cash or S/O?
Cleaner: No, a transfer on the day is fine.
Second occasion...
Boffin: So, sorry X I have noticed I have overpaid you again. I’m really sorry. My head is all scrambled this week (Son’s death anniversary). All my regular payments are automated because I have a cauliflower brain at times.
Cleaner: Suppose you want it back?
Boffin: Yes, but it’s my error so I don’t want it to cause you any potential hardship. Would you like it off in small amounts like I offered last time?
Cleaner: Just leave it off next week. It’s fine.
Boffin: Are you sure?
Cleaner: yep.
Boffin: I really need to set up a S/O, it’s not fair on you for this to happen again.
Cleaner: I don’t want a S/O (explains reasons but she has confusing reasons)
Boffin: It really is no different. The only difference is that it is automated. That way I can’t bodge up.
Cleaner: Just transfer on the day is fine.
Left at that but I am setting up a standing order.
I have always given a note in a card (xmas, Easter) when given a bonus, thanking her and wishing a happy whatever occasion it is)