I agree-it's almost positively a female. Some female mollies aren't as likely to spread their fins, as irdajoh says. I think this may be the more shy, timid fish, as mollies seem to spread the fins when more relaxed. I also think that molly looks very, very pale, unless it's a color I haven't often seen before.
My favorite fish are female bettas, Balloon Mollies and Peacock Gudgeons.