How many chicks in the brooder? What is the exact sq. footage of the brooder? So, they were hatched on 7/17, and went out to the barn on around 8/14? That places them about 4 weeks old when they went out. I assume they were weaned off heat then? So, at 4 weeks, they should have been fine without any extra heat. But, if the fan was blowing on them at night, they could... might have gotten chilled at night. Not likely during the day. My take would be to give her the supplements, and then follow your gut. If you feel that she's just not right, and you are building strength and good genetics into your flock, then you could cull her. There is no right or wrong answer here. Your flock, your husbandry methods, your choice.