Where did you rescue her from? In mammals and fish, internal parasites can cause lack of appetite and rapid weight loss. She may need a fecal done by a vet to check (have to wait until Tuesday since it's a holiday weekend...and wait for a sample) I'm not 100% sure about how parasites work in snakes, but 80g in a week seems very fast to me. I also would not try force feeding yet, might just stress her more if she is not feeling well...maybe someone else will be more helpful.