A humidifier might also helped with the cracked fur.  
**I don't know much about the BML diet, and I know it is strict so please someone correct me if I give bad advice.**  
1: if she's underweight, maybe a few fatty foods (unsalted peanuts, avocados, etc) would help put some meat on her bones & give her energy.  You could also try olive oil as that's a healthy fat that's high in energy.  
2: you could also give her the fresh fruits & veggies in the pouch during the day.  That's how I make sure Fritz gets them because he has a tendancy to leave them during the night & focus on the HPW mix I give him.  
3: you could also try hand feeding her some, treat it like a treat :)  
4: maybe also provide a yogurt/juice/honey/egg mixture as a 'treat' to give her a little extra something tasty that's also full of nutrients & energy.