I'll throw my 2-cents in on this conversation. The bathroom you choose should match your equipment not the clothes you wear. You want to use the girls bathroom, then get a wacadicoffamy surgical procedure.
A huge number of transsexuals live that lifestyle not because they have a true conflict with sexual identity, - most want to keep their male equipment. For these its largely part of a sexual fantasy they live out. Many of these are not gay at all, and have the same interest in girls as you and I. Some are even married to women who have excepted it. Bruce Jenner comes to mind. Others have taken a very perverted path, working in porn and prostitution. Now I did not say "all", but it is the truth that there is a large number of these people you really really really don't want in the bathroom with your daughter or wife. If you are going to have a policy that transgender / transsexual people can use a girls bathroom, you are opening Pandora's box.