Ds3 had both and the fit was WAY better in the PWSG. The new shoulder belt guides in the SGL made the belt sit at the edge of his shoulder and the lap belt was too high. I constantly had to tell him to sit straight and get the belt back on his shoulder in the SGL. The only thing that was better was the SG clip but for a girl I wouldn't think it would matter. Ds only complained once about it in the SG and I just let him take it off since the belt fit was good. He needed the clip in the SGL to hold the belt down.
Here are some comparison pics. In the ones of ds2 sleeping in the SGL the headrest is in the correct position for him sitting properly, he would just get slouchy when sleeping in the SGL but not in the SG.
PWSG winter early 2011, 5.5 yrs old and about 46 pounds, 47 inches. He was turning towards me a little so the shoulder belt seems a little off.
PWSG Fall 2011 6 years, 3 months 50 pounds, 48 inches (when measured in June.)
PWSGL. 6 yrs 50 lbs, 48 inches
PWSGL 6 yrs 3 months
He only used the SGL those times pictured in our truck and I sold it to get something else because he was so slouchy and I wasn't happy with the belt fit.