Confused about my sister?

Okay, so recently I stumbled across a hidden folder on my sister's computer filled with pictures of naked girls. Does this mean she's a or biual? She's always been a tom boy, but she led us to believe that the reason she doesn't dress up is do to her being overweight (kind of like she has self esteem issues) and she has a HUGE crush on the rapper Nelly and she's been obsessed with him for years. And, when my mom asked her if she was a once, she denied it and was angry at my mom for even suggesting it. But, my mom also told me that my sister went through a "phase" when she was younger when she thought that she might be gay (she told me this when I confessed to having feelings for other girls). So what I'm thinking here is that my sister is in the closet because she thinks my mom won't accept her (because of our religion) and is just waiting to get out on her own? Anyway, I'm just really confused. I'm (or at least bicurious), so if my SISTER is bi (or gay) too, then is ity hereditary? Or is it just a coincidence? My mom also confessed to going through a bicurious "phase" when she was younger, but that was because her sister molested her (her sister was d, also). I know uality doesn't have anything to do with being ually abused, but being molested sparked that curiosity in her. So yeah, I'm not even sure what my question is anymore. I'm just so confused!