My friend said that they were gay on Facebook?

[Chaz]

Depends if you are still in touch on a regular basis. If you are, then you could either ignore it and wait for her to say something directly to you, or add your own comment about she was your best friend and that you value that above anything that nature decided well before any of us were born. Doing nothing would be my option unless we spoke regularly.

Maybe also, you might want to consider your own views on the subject. You sound like a compassionate person, so hopefully you are aware that anyone's sexual orientation is innate and not a conscious choice. Maybe your friend is just realising what her instincts are telling her, or maybe you are right, that some dumb friend has compromised her profile. Best to keep all your options open until you are sure.