Well, I think I would like Dalia equally well as a human (though of course she would be rather different, simply by virtue of being a different species), but her general personality does mesh very well with Peter. They are... hmmm... restful together, is the best way I can put it. They do idealize each other, but they also try to live up to each other's idealized image and support each other when they falter, so it works out well -- it's not blind idealization, if that makes any sense?

Of course, I am coming from a position of writing a lot of OCs and am therefore -- both as a matter of principle and as a matter of self-defense -- of the opinion that pretty much any OC can be done well, if the writer treats the character as a real person (despite whatever outlandish traits ze may have) and is realistic about the effect that OC would have on people around hir. But yeah, in terms of general audience reaction, it's unquestionably easier to have Dalia be a cheetah instead of a human. *sigh* In fact, I suspect the main reason I myself avoid Mary-Sue accusations is that I'm not inventing OCs to partner with beloved canon characters. *deeper sigh*