This is lovely! It's a treat to see the wizarding world through Augusta's eyes, and I love how you show her onetime friendship - almost more - with Pomona. It's a neat glimpse of these two not only now, but in the past.
The opening is wonderful for the way it shows Augusta's quickwittedness and courage, but also her dedication to house and family. At the end, with Neville talking happily in Pomona's house about her plants, that family harmony that Augusta so values has been beautifully restored.
I can't imagine that this redoubtable woman would have it any other way. I fancy that the style you've written the story in also conveys Augusta's character just in the shape and sound of the writing: she's practical and observant, but truthful as well, and kind. She believes in order, but is willing to make changes when it's time (the hat! And moving from widowhood into a new relationship). But most of all, Augusta is very private, calm and focused on taking care of her family.
For now, they should have tea.
Great, great ending! And great story. I think I'd really like to see more of Augusta and Pomona in this Boston marriage. You've brought this unexpected pairing to life in a way that makes it seem inevitable!