no weight gain

[Greywolf]

I have a problem , i just inherited a nice savannah monitor , she has been fed solely on chicken livers , ,chicken , beef , rodents and dog food for the last 7 years (from what i was told) each time she was fed she received nekton-rep vitamin /mineral supps as well , i have this lizard now and have her on rodents , but she seems to have no weight gain at all , and she is verrrrrry thin , but has a ravenous appetite, any suggestions from anyone please ?