Dull, lethargic chick

[Tiana's chickens]

Hey guys, I'm back 8 weeks later and my poor girl is showing symptoms again. So her symptoms are lethargic, not eating or drinking, crop not emptying and bloody poo. The exact same symptoms she was showing when she had coccidiosis 8 weeks ago so I think she's got it again.
I have some medication left over from when I took her to the vet last time. Should I go ahead and treat with that?

 

[Tiana's chickens]

I was kinda hoping she would be immune to it cocci by now (she's 18weeks).
I also keep her shed pretty clean and they free range everyday. She lives with 5 other chicks a week younger then her and she seems to be the only one who got the coccidiosis last time and this time too. Why is this? Does she just have a weaker immune system? Or maybe because I bought her when she was 6 weeks where as a broody hen raised the other chicks as day olds so maybe they are immune

 

[Tiana's chickens]

Also I found round worms in the coop so I treated all with a bird wormer called levamisole

 

[Tiana's chickens]

I found round worms about a month ago*

 

[Tiana's chickens]

I think I found where I went wrong last time, after the treatment I didn't give her any probiotics to restablish the healthy gut bacteria.
I put her back on the medication and she is recovering again, this time I will give her probiotics after the treatment and hopefully she won't get it again