she didn't agree with the redefinition of the word marriage - as far as she was concerned it was defined in the Book of Common Prayer as a union between a man and a woman, and it couldn't and shouldn't be changed.
Fast forward to right now, with the word 'woman' apparently up for wholesale redefinition, and I can completely see where she was coming from.
There's a crucial difference. Marriage is a social and cultural construct, but some form of it seems to exist in most societies (largely because it's tied up with concepts like property rights, inheritance, which children are legitimate, and also it's a handy way of controlling women's reproductive capacity). The C of E and the Book of Common Prayer don't have a monopoly on what it means.
"Woman", on the other hand, is a word that has an external referent (unless you're a hard-line philosophical anti-realist): it refers to the people like us, with uteruses (for the most part, whether working or not), vaginas, ovaries, etc.
It also has social and political implications of course: we are people with a shared biological reality which has (due largely to the actions of men collectively) political consequences for us, many of them adverse. And a huge history of sexism and oppression on the basis of our biological sex behind us.
You can't change the meaning of the word without (a) denying biological reality; (b) removing a voice to a politically oppressed group and (c) engaging in massive historical revisionism (again with bad political consequences for women).