Unlike others, Seven hasn't put much thought into sexuality and gender preferences. She thought about it briefly when undergoing the Doctor's relationship training and attempting to date one of the crewman aboard Voyager, but it was never something she put much weight on. Perhaps because it didn't matter the way it did in Earth's past, where religious and social overtones clouded one's perception and put expectations on something biological that could not be altered, no matter how much one wished to change it. Where Seven's from - or when, rather, it doesn't matter and hasn't mattered for centuries, especially now that humans aren't the only ones out there.
Rose has a point. If she has to do this, at least it is with a friend and not someone she objects to, like Tony Stark. (Too bad she'll be smooching him later.) "Perhaps it we should see to the kiss before the robot lessens the parameter of the force field."