Here is what i have on the holster based on the figure, which seems to match what we are seeing in the movie pics.
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here is my sketch of what i am seeing, sorry i'm not much of an artist:
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1 - this is on top and separates the barrel and the smaller part under it. I'm guessing this loops around to the back and probably keeps the thigh strap in place. It may also just be one long piece that goes up the back and loops over the top to hang from the belt, but that is just speculation, since we can't see the back of it.
2- this is the smaller rectangular shaped right side flap that is sandwiched in the middle
3 - this is the larger sloping left flap that is in the back where the 3 parts overlap. I think from where it folds to the bottom of the holster is probably no more than 3 inches - the approximate size of the blaster body.
On the figure and in at least one of the movie pics, you can see some attachment method for the thigh strap on the front of her thigh. But i cannot tell how it works, if it is a buckle, or something snap-like, or just studs with holes. I can't tell.
Check the pics and let me know what you guys think.