Out of 4 monkeys I got, one developed a problem and had one do this; pedialyte, Lafeber carnivore diet, eventually had to give Baytril diluted one drop on back for five days-a reptile vet can make this for you. After that treatment his weight caught up to the rest of the group in about 3 weeks. Your new girl may have had a low grade bacterial infection so I would treat her too; maybe all of them?