I watched the show when it originally aired on UPN, and I have to admit, I thought that’s all she was for. It was UPN, after all, and that network wasn’t afraid to be sleazy if it boosted ratings.
I was very happy to be proven wrong. She turned out to be a genuinely interesting character who enabled some great stories.
Oh they totally did hire her as eyecandy. They just also happened to write her character really well so they got to eat their cake too. She didn't even want to do it, but, IIRC, Obama convinced her to do it just because it's Star Trek and would be great for her career.