Hello~
It seems like a couple of things could have happened.
First, the bite could have hit a nerve, this would cause the pain when trying to move the hand.
Second, the bite could have caused her extra anxiety, the sudden action of the bite can startle a person, this is turn can cause anxiety, not to mention the stress of trying to break up a fight. The anxiety could be causing some of the issues you mentioned.
Having Fibro and degenerative discs does not help either, the immune system is not as strong as it is in folks that do not have these issues, so, again, these symptoms can come into play.