Hopefully it's a vitamin deficiency and she will recover in a short period of time.
When to put her back in the flock would be up to you. You would need to determine how well she is able to move about, to get to food/water and is eating/drinking well enough to be out of isolation.
If you find she won't drink the vitamin water, you can use some of it to make her mash.
As far as giving vitamin water to the rest of your flock that's totally up to you. Extra vitamins now and then won't hurt.
When to put her back in the flock would be up to you. You would need to determine how well she is able to move about, to get to food/water and is eating/drinking well enough to be out of isolation.
If you find she won't drink the vitamin water, you can use some of it to make her mash.
As far as giving vitamin water to the rest of your flock that's totally up to you. Extra vitamins now and then won't hurt.