Yeah, it took me a while to realize they were not exactly in order of easiest at the top, an hardest at the bottom with the flirts.First off, a date. You can do more if you want, but a single date will work just fine.
Next, flirt with her every single chance you get. Rub her shoulders over and over again. This drives up her love stat.
Finally, just be patient. She'll actually let you do a lot of things fairly early, but remember that the MC is tailor made for seducing Rogue, not Kitty or anyone else. You jut have to be patient and keep working her. She'll come around.