Hi
@RAsChickens
It's great that you pay close attention to your flock, this way you will be able to detect when something is going on.
Take time to watch their behavior so you can become familiar with each one's little "quirks". For instance I have a Barred Rock that comes out every morning, eats and drinks a little, then she hops up on a perch in the run, preens a little bit and then I see her take a quick cat nap. Eyes closed for about 10mins, she snoozes -LOL Then off she goes (she has done this since she was a baby). Another girl I have, first thing she does is make her rounds around the run, closely inspecting the fencing and ground for any spiders, ants, crickets, etc. that may have entered her territory during the night - all intruders are promptly consumed

These are the things I look for every morning - chickens (at least mine do) have a routine they follow pretty much every morning, unless
I change something up. If they are not following their routine, then I know something is up.
As for your girl - sometimes they do just stop and be still - just do nothing. Don't know why - could be just enjoying the way the cloud looks, they might hear a bird singing - who knows

When to worry is if any odd behavior continues, then it's time to investigate. I do understand that chickens are addictive

Take time to enjoy each one everyday, relax and spend a little time with them - once you have learned how each one acts, hopefully it will ease a bit of your anxiety. Anytime you have a concern, please let us know. Photos are always welcome.