Please Help, My chisken's toes are falling off

[HopefullyFULLER]

My hen is about 2-3 weeks old and she was perfectly healthy when I put her and my 7 others it’s 90 degrees out here in East Tennessee (my babies are spoiled by the way) inside in a tank with soft bedding etc. This morning we get up to find my baby missing the very tip of her toe is black and MISSING!! No injuries have occurred to my knowledge and I don’t see any other wounds please help!! I need to know what this is!