While it does not happen often the more animal you have the more you are bound to have a truly picky one that will frustrate you, trust me I have one like that she will eat for 2 to 3 months straight if even that and than nothing for a year, that's what she does and as long as she is healthy and doing well I just let her be.
They are all different and obviously some get by on very little food and there is nothing you can do about it no matter what you try.