I bet your remaining flock is not sad! It is hard and miserable to have chickens bullied. It was a good decision to put her in that bigger flock. Not every bird likes or tolerates being kept pampered. Personally I enjoy my flock so much more when there is peace in the flock!
As for the other place, a lot of chickens look like hell this time of year as they are going from through the molt. What I see is a thriving chicken community in a lot of lovely space. Those birds look alert, active and content.
Looking at your pictures, that type of bird needs a lot more space. Spoiling does not make up for a lack of space. That bird IMO will be miserable in a smaller set up all alone. She looked happy as can be where she is. Space to run, other birds for company.
And birds hate change. She looks well adjusted, leave her. I think she is happier in a bigger set up. You might be sad, but she isn’t. You really want what is best for the bird.
Mrs K