The way I read it is it's about the tiring, silent, unnoticed 'women's work' that goes on in the background, and that is undervalued and unrecognised. There are also scattered references to small kinds of folk magic, the kinds of stuff that witches are always portrayed as doing in weird little folktales from around Britain and Ireland (knotting horses' tails, gathering dew, dancing on frost-covered grass with feet smeared with fat to protect against the cold). It's a small, homely kind of magic.

I also see resonances with a medieval Irish poem normally given the title 'Lament of the Old Woman of Beare' in English. Here's a link to a translation, although I'm not sure if Samatar was alluding to it in her poem. Ignore most of the rubbish written online about this poem (it's all 'sovereignty goddesses' and 'mystical Celts' and is complete nonsense), and you can see that it speaks from the persona of an old woman lamenting the passage of time, initially mourning the loss of her privileged youth (when she ate and drank well and was loved by kings), and ultimately being reconciled with her age and impending death.

At least, that's what I think is going on in 'A Visit With Morgan Le Fay'.