So... I've actually done something like this.
The o-shot specifically refers to the injection of prp into the superior vaginal tissue - usually near the 'G Spot'. The G-Shot is the same idea, but using a filler material (collagen usually).
I've done basically the same thing, but used saline, instead of either material, since I don't have what it takes to synthesize PRP, and I cannot buy collagen. I also don't have access to or use local anesthetic - so I've only been able to do this with 'patients' that also enjoyed pain stimulation - even though I use a tiny (33g) needle, it's a VERY sensitive area....
The idea of how this works, as I understand it, is the 'G-spot' is an unusually dense collection of nerves situated in the superior vaginal tissue. Injecting anything into/superior to this set of nerves creates a pocket of fluid, which, simply because of its volume, pushes on/compresses these nerves, which then leads to increased stimulation.
The patients I've done this with have reported this to be the case....but in my case, it's of limited application because: 1) I do not have/use anesthetic, like most doctors use, so it's not comfortable for the patient....sometimes that's the objective though.... and 2) I use saline rather than either PRP or Collagen, and so the effects are VERY temporary - the saline is fully absorbed within only a few hours, and the benefits are lost thereafter.
(note: this is NOT a good idea to experiment with)