As long as your chick is acting normal, eating and pooping, let's not do anything right now. If it was an adult hen, I would tell you to begin treatment with an anti-yeast cream, but sour crop is rare in chicks and I'd rather see if she'll get over it on her own.
If you've been providing food 24/7, why don't you remove the food as soon as it's night. Let all of the chicks have time to empty their crops. In fact, this is more normal than letting chicks eat all day and all night. Maybe this chick just needs to rest her crop.
Anyway, her crop should be empty tomorrow morning after not eating all night. If the crop is full and squishy in the morning, then I'm going to advise you get some women's vaginal yeast treatment. It's inexpensive, over the counter at any pharmacy. Get the cream, not the suppositories.
Squeeze out a dollop the size of the tip pf your little finger, and place it inside her beak, then massage it down her throat like you do when you give a cat or dog some medicine. Give her another treatment in the evening. Do this for at least three days, more if the smell continues.
So, first of all, do nothing but withhold food tonight. Check crop in the morning. If empty and flat, she's well, and you'll not do anything else. If full and squishy in the morning after not eating all night, start the yeast treatment.