Im not really sure what multis is but you do not mention what you were feeding her before the multis...

I have a cinnabelly that was almost the same. She would eat a F/T rat once every 3-6 weeks, despite being offered every week. She wasn't gaining either. She wasn't losing weight but she stayed at 700g - 720g pretty much for 9 months. She also had really bad sheds and wasn't as active as my other snakes. I now feed her live and she eats weekly now. She seems to be a lot healthier now too. Her last shed was in pieces but all of it came off finally. She is also more active at night. I am not saying you have to feed live but it is an option to think about.