I kind of have my thoughts on Katherine Hillard and how I ended up disliking her for some time, even if as a character she was a pretty likable person. So what's the big deal? First and foremost, she became the replacement of Kimberly Hart whose relationship with Tommy Oliver kept the show going for some time. Why Amy Jo Johnson left the show is something I'd like to know. So because of that, I felt like the whole show tumbled down, losing the famous match-up and it did happen.
When? In Zeo, thanks to some immediate bad writing, Kimberly Hart dumps Tommy Oliver for another guy with a Dear John letter, which really was a frustration (that just wasn't like Kimberly Hart for a start). It was probably due to the fact the actress Amy Jo Johnson didn't show up at all so the writers came up with a rush script. Still, they could have just kept Tommy Oliver and Kimberly Hart in a long distance relationship. I felt like her relationship with Tommy Oliver was a bit forced, plus I disliked the fact that one episode of Zeo featured her as Tommy Oliver's wife in the future and NO future episode contradicts it. In Turbo, the relationship continued but fans are left to assume the fate of it, when she left the set and the other four members found new successors.
So far, I believe that while her existence was necessary to keep the series going but that Dear John letter may have caused her to go underrated. However, jump the shark as it was with her kind of forced relationship with Tommy Oliver (sadly, Amy Jo Johnson never came back so my favorite couple disappeared), the events that happened here concerning a change in relationship can happen. After all, life isn't perfect at all and they were but teenagers back then. :-P