Visit with the mother in law went well. Me and the boy were nervous when she arrived, shook my hand formally, and gave us a big blanket with the Virgin Mary on it, but the first night I overheard the him telling her how I was supportive and important to him, and she warmed up real quick. Then she made me sweet tamales with nesquick and cherries and chocolate syrup, which I had never even heard of, but were tasty once I mentally recategorized them as a type of muffin.
Me being trans never even came up (at least not while I was around), and on the last day I just got the normal mother in law experience where she just criticized how clean I was keeping the house and told what kinds of dinners I should be cooking for her son. It was a lot, but in a gender-affirming way.
Lady has a history of homophobic comments so we were hella worried, but we think she might have expected me to be like, a dude, rather than just a shy nerdy girl who is more "traditionally feminine" than his tomboy exes.
Probably will be a long while before I see her again, so glad I left a good impression.