biophiliac
Rest in Peace 1953-2021
Without other chickens - you are her flock. I think being alone makes them nervous. 
ETA: Do you have more?

ETA: Do you have more?
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Yes! I definitely feel like part of her flock lol. I don't know much about chickens, but I'm perceptive enough to know she wasn't happy, not fully. She was happy enough to begin laying eggs for us about two weeks ago... Give or take. But she would get lonesome and call for us. I've spent a lot of time with her the last month she's been with us.Without other chickens - you are her flock. I think being alone makes them nervous.
ETA: Do you have more?
You keep saying you dont know about chickens but you are sure doing right by her!
A secure run to keep them safe from predators and 'roaming gangs of poultry bullies' when you cannot be present to supervise free roaming would be ideal. Look into deep litter for the run to keep i pleasant and healthy for the birds.
They will get used to being confined and will be happy to roam for a bit when you can supervise. Shake a can of scratch or BOSS to lure them back in.