I also weigh mine every week. It really just depends on the snake. Some can eat weekly and grow a lot while another on the same feeding schedule grows slow. I have two girls that both eat the same size meal weekly. Both were about 400g when I switched them to live weaned rats. Both eat like champs. One is about 550g and the other only 475g.
If your snake is pooping weekly, that will make your snake weigh a lot less. Mine only poop every 2-3 weeks.
As long as she's gaining weight and eating well, she's probably right on track.