Hello!
Mine is supposed to be 6 months old (and I am willing to believe that!) and he's roughly the same size as yours and weighs 210 grams. He get's a rat fuzzy (about 20g) every 5 days.
Seeing that yours was scared of eating a small mouse, could mean that she has been fed pinkies only so far and that would explain why she's small-ish. So it's perfectly possible that yours is indeed four months old. Now she gets bigger meals she will also grow faster.
And let's not forget that each snake grows at a different rate