That seems to be a non-sequitur, but in any case:

17% of "tech" employees at Google are women (worldwide): http://www.google.com/diversity/at-google.html#tab=tech

18% of CS degrees are earned by women (in the US): http://nces.ed.gov/programs/digest/d12/tables/dt12_349.asp

so women are not in in fact over-represented among Google engineers, at least by that measure.