I really, REALLY love your art work and style. Infact I envy it over my realism. I do have to say I have never liked girls with short hair, I have been a huge long haired girl kind of guy, but this... Your art really makes me think twice :) again, thank you for your beautiful art.
I like the short hair. I agree with the poster above that I prefer long hair on a girl. But if you carry over the TG theme from the sister image I think the short hair fits better.
For me hair style is a bit along the line of clothes. If somebody were to change gender why would their clothes or hair style change? Over time yes, but those things are sort of separate from biology.
The choice to keep Allison short-haired reminds the audience that she once was male (even though her short-haired 'do has a decidedly girlish look to it)and was forcibly changed into a female to become the sex slave she now is for the demons she now serves.