What could be the reason this girl is treating me differently...?

I've never asked about her sexuality so idk what team she plays for or if she plays for both but she has stressed plenty of times that she's a supporter of LGBT rights. However, I've noticed she tends to be friendlier towards females who look female and males who look male (regardless of whether they're gay or straight). I am a female lesbian who dresses in a guyish manner and although she obviously doesn't discriminate, she doesn't treat me the same way she does the others. Almost like she's slightly uncomfortable being around me. Why would someone who supports the LGBT community act like this?