Three things about that:
1) That time frame is based on her being 80% sure the vaccine will work and everything going perfectly after that. The 20% where the vaccine doesn't work and the extreme likelihood of things not going perfectly afterwards is huge room for error and delay, even assuming her assessment is correct, which it may well not be.
2) As she says, having it "ready" for September would depend on the government putting in the resources to begin mass production before the vaccine has actually proven to work. Which would be a questionable move on the government's part, to put it mildly.
3) It's hard to imagine that a vaccine developed so quickly that mass production starts before we even know it works can have be tested and trialled to the usual standard in terms of identifying negative health impacts from the vaccine itself. So it would presumably be extremely high risk as vaccines go?
Based on the qualifiers she mentioned and basic logic, I would still imagine that having a vaccine ready in five months is completely unrealistic. She's described a best case scenario that I struggle to imagine is in any way plausible. As has been said already, even the 18 month time frame would be very fast.