How did the she- elephant Topsy die shockingly, and why?

She was electrocuted, she was beleived to be a bad elephant but in fact was being abused by her trainers whom she killed. Interesting story, Fred.

And Edison had a film made (which you can find with a search engine ) to show the execution. As your link says, Edison wanted the publicity to do down his rival. He wanted the world to call electrocution 'westinghousing'.