I liked Shira's character, even though by the 4th movie I was starting to worry that they were just milking the whole thing. Even as a villainess, she was likeable, and her conflicted feelings for Diego, though certainly not uncharted territory in the entertainment industry, were appreciable. Also, the fact that they didn't try to overstate or exaggerate her design - like, for example, they did with Buck or most of the sloths besides Sid (although actually Sid is a pretty drastic caricature of a megatherium too, but I digress. They just made a saber-tooth, gave her some elegance, and boom; there she was.