Big bald spot, and getting bigger...HELP

[bdn3]

I am a relative newcomer to the world of backyard chickens. We got 7 RIR hens around the first of April this year...I was told they were all the same age, around 5 mo. old at the time. All was going well and we started to get eggs around the first of May and have worked up to steady egg production of 4 to 5 eggs per day ever since. My question concerns one of the girls. She seems to not be progressing/maturing as the others did. Her comb and wattle have not changed in appearance since we got her and are still very small and white. She now appears smaller than the other birds. About a week ago, we noticed a small 'bald patch' on her back, right in front of her tail feathers. This bald spot seems to have gotten bigger in the last week and now encompasses about 1/4 of her back. We looked at all the girls carefully and we see no signs of lice/mites. We have tried to observe them to see if someone is pecking her, but it does not seem she is overly abused or mistreated. Is she sick?..the slow/non-development is what concerns me the most I guess...any feedback would be appreciated..

 

[jeepgurl]

i wondered about this too. a few of my girls have that. i just assumed that the others were pulling them out. i would like to know if that is normal too.