I dunno, I'd say there's a fair amount of evidence for Luke and Phasma's offscreen tryst.
Don't know about onscreen, other than them purposely undermining the character so people didn't expect it? Even Plinkett/Red Letter Media (who is a very smart guy) wrote off Phasma as a joke in his review (he liked the film though, just like I did), so if that was their intention, they did it well.
Offscreen reasons? Yeah. Disney makes a lot of money selling toys. Disney makes a lot of money selling toys to girls. Disney can DOUBLE their profits doing the same thing Lucasfilm did in the first trilogy and by getting lots of girls to like Star Wars to.
The original trilogy resonated with boys and men due to the father (henchman not the main villain) and son dynamic. Disney can do the same thing with girls and a mother and daughter. It is a basic thing that every girl can relate to, just like every boy could relate to. Whether you had an awesome father, where you are glad he is not like Vader, or a bad father or wish you had a father around. Same dynamic can work with girls.
Will it work? My mom (who is really old) loved the film. My sister always liked the films (except the prequels) but liked this one more. I am sure if you walk into a Disney Store they are marketing the heck out of Rey to girls.
Gender also does not matter with the force and neither does size, so they will not lose the boys. Brilliant by Lawrence Kasdan, but he was always brilliant and he is who wrote Empire and Return of the Jedi and Raiders of the Lost Ark to start with, not Lucas.