BO pullet not acting right

[wac]

Have 26 BO pullets 8wks. old 1 is sitting around more than normal like napping. I notice this yesterday but other times she seem normal going out in run with others. All the others seem fine. This evening she was in coop sitting by her self with feather fluffed up a little like she might be a little cold. It is a nice day here in the mid 70's should I be concerned. The for your advice.