Problem with a 4 week old chick

Hi all,
I'm a new chicken keeper and have a chick that has had vent problems since we brought her home. We currently have 8 chicks total (including her) and none of the other chicks have a problem. She had pasty butt originally, but that doesn't seem to be the problem anymore. After reading through some other subscriber questions, I thought it was vent gleet so I added ACV to the water, made sure the brooder wasn't too hot, and made sure the water and electrolytes/probiotics I was giving them in a separate water container was at room temperature. I also have been applying anti-fungal cream to her vent, but that doesn't seem to be helping.
I am feeding them an organic starter now, but started them on a medicated feed, which they got for the first week and a half that I had them. The chick in question is eating, drinking, and acting normally in accordance with the other chick, but she is not developing as fast. All the other chicks are molting and getting new feathers more so than she is and she is smaller than the rest of the chicks.
Sorry for the long thread; I would appreciate any help or suggestions you may have. I just feel bad for her not knowing what to do. I have attached a photo of her vent and what it looks like every morning. Her bottom is also not covered in a lot of feathers and has been like that since I got her.
Thanks in advance for any help you can provide!
Lindsey (worried chicken mama)

 

Nice to meet you too!