The Ghost Recon novels would like to argue for the existence of female Ghosts. I have read both of them.
The first one has two female Ghosts. Major Gray is actually the person that recruits Captain Mitchell to the Ghosts in the first place, and is a command officer at that point.
Alicia Diaz is the team's marksman in the first novel, and participates in the mission.
She breaks her ankle prior to the mission in the second novel, and is never mentioned beyond that.
Her bio lists her as being part of GR2, GRAW, and GRAW2, but I don't remember them in the PC version of the game: http://ghostrecon.wikia.com/wiki/Alicia_Diaz
In addition, since Ghosts are off-the-record, they could technically be allowed to have females regardless of the fact that standard US military has MOS gender restrictions.
PS. The second novel is garbage. I would suggest never acknowledging it exists, because it ruins any reputation of the quality of people recruited to the Ghosts.