With enough witnesses for provocation, the bully will find out that her management style was at fault. But a really good upper-management person, when finding out that others felt there was provocation, should step in and talk to the bully VERY EMPHATICALLY. When a 20-year veteran acts out after a change in management like that, senior management must realize that there is a SERIOUS - and I DO mean serious - morale problem brewing. I've seen it before.
On the other hand, I must be objective about this and point out that the 20-year veteran handled it incorrectly, too. She should have gotten up, walked to the bully's boss, and said, "This person is harassing me. Do something about it or I'll file suit against the company for harassment." Then she should have walked back to her desk and ignored the bully.
Granted, the "slap the slop out of her" approach feels better, but some companies have a "no fighting" rule that makes it very hard to ignore taking a physical approach.
If it had been me, I assure you I would not have hit her. In the face. But I would have hit her in her personnel file. Then, every time she tried to use that tactic again, I would have filed a repeat grievance. It only takes a couple of times for someone to notice.
Then again, working for the US Government as a contractor, I am somewhat protected by the Federal Acquisition Rules, which set forth standards of treatment when the bully is in Civil Service and I am not. In private employment, we had to resort to state labor laws when we had bullies.