Feeding my caftan obsession...
Sources for Anglo-Saxon women's clothing in the conversion period is scanty. There's some good stuff, but you're in the awkward period when they were starting to bury folks in Christian shrouds, but before a lot of manuscript illuminations are getting made. One source Gale Owen-Crocker points to is the Genoels-Elderen ivories, which have a scene of the Visitation. I don't want to yank the photographer's picture, but here's a link to a really good shot. Mary and Elizabeth are wearing open-fronted long jackets with decorated edges and bands on the arms (or the jackets are short-sleeved, and also decorated gown sleeves are showing - you really can't tell). They have on long rectangular (I think?) veils, open at the neck, which look like they may be worn over a coif of some kind. They wear narrow belts over their jackets.
The current focus of my interest, though, are the undergowns, which are gathered or pleated across the front. I'm not sure if this is an actual fashion feature, or an artistic tradition - earlier Mediterranean models for this image show more Classical-style drapery with lots of folds. On the other hand, this is pretty detailed and tallies well with Ottonian fashions (as far as the placement of decorative bands on the arms and such goes).
I poked around the Internet a little bit, reading up on pleat types. Cartridge pleats or simple gathering seems like the most likely thing for early stuff. All the knife pleats and box pleats seem to be 15th or 16th century.
I have some heavy white linen I've been saving for an undergown, and I tried cartridge pleating a section of it. The result was not that great. The folds in the ivory seem pretty big, and the cartridge pleats went in pretty small. And then they poufed out immediately, so that there wasn't much of a "fold" look going down the cloth. Also, not sure if a pleated/gathered front will be a good look on a short fat lady.
Alternatively, it might work better on a finer or lighter fabric.
Addendum: I looked at some of the other figures on the ivory and have two thoughts: