Got it in one! Had a lot better of a time figuring out Limestone, probably because I've doodled her a lot more than Mac? I tend to do a lot of shite sketches that you lot will never get to see because they really are awful and taking pictures of them and uploading them is too much of a hassle. They do come in handy for stuff like this though, because it means I only had to draw Limestone properly once to be happy with the result.
Speaking of, I like to think of Limestone as being pretty small; everyone always headcanons Pinkie as being pretty tiny and I think it's funny to apply that to her sister as well. Unlike Pinkie, though, Limestone is fairly built from all that time on the rock farm, and now from the work on Sweet Apple Acres she does with Big Mac. She also has a bit of a side-job, but that's gonna get it's own dedicated doodle so hang tight till then for that.
Also, unlike Big Mac, Limestone ain't floofy; she's shorthaired, like most ponies are, so she doesn't get fetlocks or chest fluff.
Anyway, that's all I have here, hope you like her :)