It's also possible that the pregnancy is accelerated. She could very well only have been pregnant for a few months, but is at full term anyway. I think considering this pregnancy to be of typical length, when absolutely everything else about it has been insane so far, is a tad conceited of us.
It does say on the cover of this months DWM in the UK that she is nine months pregnant, which is where everyone probably got their ideas, so while your theory is completely right, I think she actually has gone to full term