If Dixie were not a clone, it would be an a mistreatment of the character in regard to the vocabulary* Smash Bros has established. We cannot go around with characters like Mario/Luigi, Fox/Falco/Wolf, and Ness/Lucas, with Diddy and Dixie not sharing a certain amount in common. I would not only expect Dixie to be a clone ("semi-clone" to some people), but I would be let down if she were a completely unique** character. It just doesn't have any merit as a decision.
*A World vocabulary is essentially what makes a fantasy or otherwise created world believable. This is accomplished, primarily, through setting up rules and boundaries within the world (such as gravity) and establishing that it is always in place.
In contrast, worlds that do not have this tend to feel cheap and easy (unplanned), wherein, say a writer of a TV series, will write in a Deus Ex Machina (God interference right before the end) to justify the story.
**This is to say, if she had a unique playstyle which differed greatly from the base set of Diddy. A "gimmick" (I'm a big fan of these, they are essentially a hypothesis on a character played out in development), or move set that differed too much from one another, would be to disregard the way the two actually play in DKC. If she cannot be described as "like Diddy but ___," it doesn't fit.