In Power Rangers Zeo, there is that infamous and rather out-of-character Dear John letter plot. So I would probably want to share my thoughts on Kimberly's legacy first since I think it had something to do with the Dear John letter... and Douglas Sloan one of the worst writers in Power Rangers. In fact you might want to compare Douglas Sloan to Shoji Yonemura in Toei or a burned out beyond belief Toshiki Inoue.
I was thinking Kimberly was perhaps "every 90s boy's first crush" maybe if that is if they were in America. Then again, she might have also replaced every 90s boy's crush on TV in other countries too. Let's get to the point- Kimberly was pretty popular as a character though she is admired very superficially. I guess the show still had its popularity ratings and maybe, Amy Jo's resignation wasn't accepted and I felt like she wanted out of the show more than once. I don't know what the actress was thinking but perhaps, she just really started to hate the direction Power Rangers was going and I would to, if I were her considering it was already getting overextended.
So I don't hate Kat and I think she's a good character but the problem was the bad writing that came in between. So Amy Jo Johnson finally got her resignation done and over with professionally. However I guess the whole Dear John letter was probably producer's decision or Douglas Sloan's bad writing. Note that Douglas Sloan was head writer of PR Turbo's first half which was rather dull. My speculation was that since Kimberly was replaced by Kat so they felt like, "Hey we must replace Kimberly with Kat even as Tommy's girlfriend." so which really may have resulted to the "Dear John letter" which is out of character since Kimberly isn't the type to just dump Tommy like that for another man.
Or another the producers wanted revenge on Amy Jo Johnson for leaving the set so they decided to malign her character as well. Regardless, it was a terrible, terrible thing to do.