Even if she is butch, she still has the pertinent bits, How she looks may just be a matter of liking the look, the way some women hate to wear skirts.
*shrugs* least that's what my sister said. She is a lesbian, she likes the boy's clothing but she leaves her hair long, though she did shave it once.
Plus, I know from experience that the short haircut is beyond easy to deal with. Men's clothes are also really comfy, specially in the crotch, girl's pants pinch or tend to chaff.
I did the "boy" look for a while, and nothing beats it for practicality and functionality, and very few things marketed for women are as comfortable.
Specially if you have a hobby like tinkering with engines. Getting your hair caught on an engine hurts, and the work is really hard on your clothes.

Hope I was helpful ^_^