Alright, if GAF can't help me then no one can, and I'll accept that it's all in my imagination.
I remember this platformer I used to play on the PC as a kid in the mid-90s (our OS was DOS). You played as either a bipedal cat robot or a bipedal cat in robot armor, but either way the body was dark red. I also remember a lot of vertical platforming. I think the cat's name was Diana or Diamond or something. I was somewhere between 5 and 7 when I would play this and I remember being so obsessed that I wanted to change my name to the cat's name (to which my dad said "You can't do that, that's a girl's name!"). The environment was dark, like a castle with traps or something, but the overall tone of the game was pretty friendly.
There's a good chance I'm conflating details from other memories. The Diana could very well be coming from the actual Princess Di and may have nothing to do with the game. I also played a lot of Prince of Persia and Cool Spot on DOS, along with a racing game that I remember too little about to describe here.