The locker room concern is new for me, but I'll give it a shot.   By the way, I have three daughters, raised in a very conservative community of small town Iowa, and all are strong supporters of gay rights(all are heterosexual).   

The girls protesting in that link have not been exposed to transgendered person from what I read.  They are simply afraid of what hasn't yet happened-correct?    While we have certainly had some crazy over reaction in schools to state/fed regulations designed to protect students, I don't think it happens often?

If the case comes up, I would think an area for privacy of the transgendered individual would be best.  Forcing them into the shared area of the locker would seem out of place to me, for all involved

Curious, do you think a boys would object to sharing the locker room with a girl in transition to a male?   If it was my daughter, I'd be concerned for her safety for a number of reasons.