I can't understand the bold part of this sentence -
Potpourri was provided, made by Mrs. Jevons to her own recipe, to take away the smell.
What is the meaning of "to her own recipe"?
In this context, it means that the potpourri was made by Mrs. Jevons using a recipe she'd created herself.
You could reword the sentence using the word follow, and it would retain the same meaning:
Potpourri was provided, made by Mrs. Jevons who followed her own recipe, to take away the smell.
From what I can tell, it's an unusual usage of the word "to", but it may have been chosen to help the sentence flow better, or to place emphases on the fact that it's her own recipe.
I believe the phrase "made to measure" uses the word "to" in a similar way.
This is a slightly archaic form to my American ears. It means she made the potpourri from a recipe she created. The book it’s from is historical fiction about the early 20th century, and uses a writing style and phrasing more popular in that era. If I were writing that sentence today, I would write
made by Mrs Jevons according to her own recipe
made by Mrs Jevons from the recipe she created.
made by Mrs Jevons from her own recipe
The first two make it clearer that she created the recipe. That's the first interpretation I'd give the third, but it could also be easily interpreted that it was from a recipe she owned, whether or not she created it.