I'm not sure if the other parents should or shouldn't know that a transgendered girl is part of the troop. By making it publicly known, the kid is set apart from the rest of her peers. There shouldn't be a need to explain her gender to anyone, but because accepting transgendered kids into the gender-specific organization is new, it might have to be made public in order to prevent any bullying and to facilitate communication, education and acceptance rather than isolation.
Though I can appreciate the boycotting girl scout's desire and initiative to stand up for what she believes in, I don't see the value in her campaign when it functions to exclude individuals from benefiting from an organization that works to build the character of girls by education and acceptance. The video linked to the article seemed to be cut off towards the end, so I'm not sure if the boycotting girl scout offered any suggestions for communication or discussion of accepting transgendered girls into the organization (or creating a group catering for their needs), or if her solution to the issue is to straight-up exclude individuals from joining the girl scouts.
Link to article below:
http://www.huffingtonpost.com/2012/01/11/girl-scout-cookie-boycott-transgender_n_1199260.html