I bought a poster years back that covered this...
A mature doe, ie anything other than a yearling doe/fawn....will look big IMO.
The poster suggested that does were longer in the chest vs. a fawn, a fawn they assocaiated with a briefcase, and a doe they associated with a peice of luggage...
Also I think a doe's face is much longer/narrower looking than a fawn....shorter stub nose...