It does appear she has dry fowl pox.
In case you're unfamiliar, fowl pox is a slow-spreading viral disease that often affects birds. There is no cure for fowl pox, only basic supportive care, and vaccines. For the hen with lesions, I would apply an antibacterial ointment such as Neosporin or use something like Iodine on the lesions to help prevent further spreading, or infection of the surrounding tissue.
The lesions are highly contagious so avoid touching, or disturbing them too much to the point where they might fall off onto your clothing, shoes, or ground where they may be able to infect other birds. Disinfecting the flock's waterers, and feeders would not be a bad idea as well. If the others are already showing signs of fowl pox, I would see no reason to separate the main hen from the flock.
In addition to the treatment suggested above, you may consider administering vaccines to the whole flock. While it won't cure the birds that have it, it may help prevent further spreading within the flock.
You can find vaccines here,
https://www.valleyvet.com/ct_detail...q0iXFWm6d_EXaCibZkmxej-m_mPFs1BxoCBbQQAvD_BwE
And fowl pox info here,
http://extension.msstate.edu/publications/fowl-pox-backyard-flocks
