I have had 'slow' chicks like that one. I think it is what you described - a vicious cycle where one doesn't get to the feeder - not out and out 'picking' but just where one is a little bit weaker or less aggressive and gets pushed around by the others. Since they get less feed, they just grow slower, and the slower and smaller, the harder time getting to the feeder...until you have a vicious cycle and eventually the chick succumbs to 'failure to thrive'.
What I do is not to separate the chick entirely (unless there is a pecking problem), but to take out the small chick a couple/three/four times a day and let her eat all she can eat where she doesn't have to fight for food. Then I put them right back in with the other chicks. Just 10-15 minutes or so.
I use the starter crumbles and use warm water to make a mash for the weak one - they LOVE the moistened crumbles, and will go for it like candy. Also you know since it's moistened, they are getting in some needed water as well. I take the chick and set it in front of the feeder (usually a flat large jar lid like a mayonnaise jar lid) Then I dip the beak into the feed to get them interested.
Good luck with her - she sure is a cutie!
Also, to add...UNLESS they are pecking at her specifically I would NOT separate them entirely. She will be miserable as a lonely chick and that may cause as much problem as leaving her with the others where she is more comfortable. They will not necessarily start pecking on her. I've had a couple like this and never did the other chicks gang up on the weak one. Now, if they DO start to pick on her, pecking drawing blood, etc, then you will need to separate, but that is a last resort and be prepared for a very sad and depressed cheepy chick.