You could probably easily bump the size to weanlings or even small rats. The snake looks to be in good condition, but hard to tell how big she is without something in the picture for reference.
4 1/2 month old BP takes weaned rats.
Try a weaned one next time and if it leaves no "bulge" whatsoever, your snake may be ready for smalls. You could also try to make a picture with something for reference, like a soda can next to the snake.