Wow, I sure hope not.
I don't really know the answer to your question, but didn't want to not post after reading your thread. I'm hoping that she is just "the runt" as they say, and a slow starter. Sounds like you are doing all you can......have you given her free time to nurse from mom without the boys around to bully her? I would suggest doing that if you haven't already. Let her nurse BEFORE the boys do. Keep her warm.
I will say some prayers that she perks up and starts gaining a bit more. Hugs to you for all you're doing to help her along.