Well, guess what: I found another one! I still don't have an ID on her, but this one seems to be in her original clothes!
Just like #1, she has "Simba" stamped in the back of her head and her body looks exactly like the older articulated Steffi Love body, except for her wider torso. The face along with her figure made me originally think granny doll, except I can't find any evidence of Simba ever making one.
This one has some kind of training outfit, complete with shoes and socks. I suspect this is her original outfit, because the shoes were pretty difficult to get of, and both have a small split as if someone tried to get them off and failed.
(Tip: I usually heat doll shoes under the water tap before taking them off, or even just with my breath for a couple of seconds. It's quick and makes it a LOT easier to get them off without risk of damage.)
So I did a bit of image googling with sports related search terms, and came across this doll on ebay:
As you can see it's not the same doll (it's a regular older Steffi Love) BUT it's the exact same shoes (the seller has a close-up of them).
So that brings me at least a bit closer to the solution: Simba Toys, 80s-early 90s, some kind of sports/training/aerobics/whathaveyou theme. And for some reason NOT with the usual articulated Steffi body. Hmmm...