One or two fan-authors/artists presume that Subaru is somewhat insecure about her cyborg body and therefore intensely curious about the bodies of normal humans and other cyborgs; her very physical acts of affection double as efforts to explore and compare.
As for her sexuality, the only known significant male figure in her life is her FATHER. Her savior and rolemodel was a woman, and her best friend was a girl, and both of them were physically attractive. Put some handsome men in her life who are just as impressive or interesting to her as those two, and we could see how she reacts to men.