The thing is: they don't know, at least from what we can tell. They know that Ai is apparently Sherry, because Vermouth called her that, but we have no evidence that they know that Sherry is supposed to be an 18 year old teenager. Jodie questions Vermouth, whether Ai and the woman from the picture on her dart board could really be the same person, but she never gets a straight answer; she also doesn't figure why Vermouth calls Conan "Cool Guy", a nickname that is proper for someone of his age in Jodie's eyes, instead of "Cool Kid". We know that Akai knows, but we can't say the same for Jodie; Akai already figured out that Ai is Shiho before the confrontation with Vermouth, yet he didn't tell Jodie.
The confrontation in the harbor with Vermouth make it seem very likely that Jodie knows, I know. But here's the big BUT: we have never got any 100% confirmation that she knows and if Detective Conan told us something recently, then it is even something seems incredibly likely, it can't be safely assumed unless it's undoubtedly confirmed. I assumed that Conan knew that Sera is Akai's sister until earlier this year and when I asked everyone shrugged and said "But he should know, right?". Well, turns out in the recent chapters that he didn't same know. I also read about people being shocked about learning that Jodie didn't know that Conan is Shinichi in the Scarlet Return. As of now, Jodie doesn't know Ai's identity is what I'm saying.