Need more booty room in the after school pants!

I've been searching the web, but I'm still somewhat at a loss as to what the best approach will be. My daughter is 10, but tall and with a booty. How do I give her seat more room for the next pair I make? The last pair I made a size 12, hoping that would cover it, pardon the pun, but when she was playing with the dog on the floor she looked like a plumber. Not the result I want when I'm taking the time and effort to sew her clothing. :) Upon closer inspection, it seems like the front is a bit baggy in the crotch area, even though it is sitting at the right spot (i.e. Not low rider in front). The back is tight in the bum and is too low. Is it best to lengthen the back inseam? Or make an adjustment in the yoke piece? If I alter the inseam, do I need to alter anywhere else? I found this one blog reference that helps me to understand better what's going on, but I am not sure how to apply a change to a pattern with a yoke. http://www.afashionablestitch.com/2011/sewalongs/discussing-at-length-crotch-length/ Thanks!