Why does your transgender friend obsess over being girly but acts like a guy?

Sometimes it's because that's what society has taught us a man or a woman should do: if you spend 15, 20, 30 even 40 years hiding being different, habits die hard. Another reason could be hormones: the mind could be female but the reactions that come from the body are 'male'. When HRT has been going for a while (years) old behaviors extinguish and disappear.

Another theory relates to the fact that a transsexual is not born the opposite sex and they although wish to be like that and they would be both happier and healthier if they were, they didn't grow up with the same input from family, friends and society as the girls did. There's no avoiding the fact that this has changed the person to be different from whom they would be if they had been born with the 'correct' sex parts.

This isn't to say they shouldn't be treated as the intended sex, but that you can't deny the changes in a person due to experience. Until mis-matched sex/brain is diagnosed basically at conception, there will be a difference in transgendered women and 'birth' women. As a friend I wouldn't obsess over this, just accept that they are them and have fun enjoying their company.