She may just be a loner! 

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Yes, only one side. Sorry, I just realized I could reply directly to the comment. Still getting used to this. I posted a photo of their set up.85 would be better.
Are you heating only one side....so they have room to get away from the heat.
Too much heat can cause them to develop slower..this one chick may be having this problem.
Definitely. Is that a liquid? Or food? I've been watching heat and if they're all squished together under that lamp I'll lower it. If they're squished over on the opposite side I'd raise the lamp. So far I've been able to keep them pretty even and seemingly happy. Is that a good way to watch the temp? Or would you recommend just keeping it at a set temp?Your brooder looks good, I am glad to see you are not heating the whole thing.
Can you pick up some Nutri Drench for her?
They are on our enclosed porch. Nights are 50's, days are 60/70's. We can't bring them inside because we have two hounds...... self explanatory haha. Thank you for answering back with me so quickly, I really appreciate it!Sounds like a good way to watch it to me...you should probably use a thermometer though.
Are they indoors?
What is your weather like?
OK. I'll do that. One more thing, if she is getting picked on, what can I do to stop that?Ok...outside it fine.
Sounds like you are doing everything good.
You may want to make sure no one is picking on her..she may just be a slow grower.
Keep her hydrated.
And I would try some poultry vitamins...they won't hurt.