So there are two ways for my headcanons about her. First is she is either Toichiro's age, a year younger, or one year older. This is just for my "i put them in the same school together so Toichiro can be awkward with his feelings while she very obviously has a crush on him" thoughts purposes.

Second way my headcanons go is her being 6 or 7 years younger as to maintain the traditional married couple sentiment. It could tie into her staying with him for so long while not openly questioning his crazy plans that are coming to the surface more and more each day. It's that he has more power in their relationship, up until she finally confronts him and leaves him, because he refuses to change.

These are just two approaches that I like. One because I can make it a bit silly and sweet, and the second to be more realistic maybe, more bitter and sad. Which isn't far off from canon I think, their original story always makes me sad.