My thinking would be that she may have eaten shortly before you got her. If she was measured right after eating it seems that the weight can be skewed by the rat body in the snake. After digestion some of that weight gets dropped. They can also drop an alarming amount of weight after a bowel movement, since they hold it for so long. Do you know when she was fed last before you got her and has she defecated recently? I always weigh Shesha the day before feeding so he has plenty of time to digest his rat and metabolize everything so that his weight reading will be more of just him and less of his prey. It seems from my experience that since they eat such large meals their weight can fluctuate quite a bit. Now if she continues refusing food, or you see only decreasing weight with no gain that would be concerning, but given the short time you have had her it seems that it would be hard to tell what her weight has been trending at. If she has only gone a couple of weeks without food it seems unlikely that the loss would have to do with that, just based on how long they can go without while losing almost no weight. If it were something like an internal parasite that could result in sudden weight loss, but again it would be a consistent trend. With my guy his weight will go (for example) 90, 105, 101, 117, 113...etc, so there is still a positive upward trend, but if you were only looking at a short section of the growth chart it could look like startling weight loss. Again, this is just a hunch, and of course you should always watch for any other symptoms or behavior that may indicate something more serious is going on, but it is certainly possible that she had a full belly at her first weighing and just recently stabilized.