The Amish were Mennonites but split off as a separate sect. Mennonites are modern. Amish, not so, last I heard and they'd be the ones with the flat brim hats, wagons, etc. I learned everything I know from the movie Witness. Ha. Plus living in the Rockies where there was a large Mennonite colony. Nice people.
There are still lots of both Mennonites and Amish dressed in black riding in horse-drawn buggies in southern Ontario, e.g. around St. Jacobs.
My understanding is also that the Amish are indeed the more recent group, but that's still going way back to a split in the 1600s.
In Ontario there are both what they call "Old Order Mennonites" and "Old Order Amish". As I recall the Old Order Amish there are still much more strict in avoiding modern conveniences, but Old Order Mennonites can have tractors and even electric appliances, and, get this, they're also allowed pneumatic rubber-tired wheels on their buggies! One of the more modern Mennonite groups (there are several split off from the "Old Order" ones) is, or was, into manufacturing and is/was a major supplier for Home Hardware (which started in St. Jacobs and still headquartered there). There's apparently lots of cooperation and sharing between Mennonites and Amish in Ontario. BTW, St. Jacobs is a great place to visit, especially in harvest season, on a weekend for country market shopping and food, etc.
I don't remember which group she was from, but I knew a woman who had left the fold, so to speak, and was working as a computer programmer when I knew her.