Giant females shouldn't be much different than males. Maybe a difference of 10 or so grams. Giants usually weigh between 100-120ish grams. Length isn't as good of a measurement as weight, but Moose (the original giant) measured 11 1/8 inches so giants are somewhere near there.
The most important thing is not how heavy or long your gecko is. It is that the gecko has the genetics to be a giant. If you didn't buy your gecko as a giant, the chances it is are next to nothing.
I have a male that weighs 90 grams and is a pretty big guy. He's not a giant, though, because it isn't in his genes. I have lots of females that weigh 80+ g. It's a normal weight for them.