Cute chicks!
She may not be eating well. The crumbles may be too large for her to handle. Try soaking the feed and making a wet mash or you can grind it up smaller almost to a powder. See if that helps.
I'd provide them with chick grit as well.
If you are really concerned, you could treat for Coccidiosis since they are 9 days old and have been outside. Being outside and exposed to dirt/environment is actually good for them.
Liquid Corid dose is 2tsp or Powdered Corid Dose is 1 1/2tsp per...
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Are you feeding chick starter and giving fresh water?
How old are the chicks?
Are all acting normal, active, eating/drinking, etc.?
Looks like wet cecal poop to me.