Even in flocks that have been together for years there can be dustups now and then or attempted shake-ups of the pecking order, etc that can lead to occasional wounds occurring. Another possibility is the bird may have picked at herself (have you checked for external parasites that might lead to her picking?), she may have somehow injured herself leading to her or the other birds picking at the area, etc. How large is the area in question? What condition is the flesh that is now exposed -- is it just bare or is it bare and open?
Once an area is exposed, it can invite picking, especially when the flesh is broken - so isolation is sometimes necessary for the sake of the bird, but isolation can also lead to re-integration issues later when you put the bird back into the flock landing them right back in the same condition.
One concern in reading your post is the use of solarcaine -- generally it is advised to avoid "caine"s in dealing with poultry. I would not reapply that and would not use it on the birds in the future.
Whenever possible it I best to keep the bird in the flock -- the use of "cover" such as blu-kote, etc can help to disguise an exposed area that may attract picking by other birds in the flock and allow for not isolating the effected bird. However, if the area is inviting picking isolation is needed until the area is healed to the point of no longer being attractive to the other birds. If you are readily available to monitor things a trial of using the cover method is more advisable than if you won't be able to keep an eye on things and remove her if things get out of hand.
Chickens are very good at healing themselves - what she really needs is to have the support from you in the form of a clean, safe environment in which to do so and the support of her body in hydration and nutrition to repair itself.
