The last two pics aren't showing for me, but from the others, I think it's a '20s silk evening dress that has been upcycled - the armholes have been cut in, on one side quite drastically into the bust - probably because the delicate material was damaged under the arms from too much charlestoning and bad storage. Then the floral appliques have been added in more recent times. The diamantes may be original or an add on too, hard to say from what I can see. I can't tell what's happening with the skirt, I think it's been altered too - do you have any photos of it full length, either hanging or being worn?
The other thing is that you will need to wear something underneath because of the wide armhole which is likely to expose your breast.