You know, I wonder if she was having a bit of the same thing as the Doctor. In S1 I always get the vibe of the Doctor trying desperately not to think along those lines, because Rose was human and all. Of course, he completely failed. Maybe Rose was doing the same thing? Trying desperately not to think along those lines, because he was this 900-year-old alien? Rose was better at it than the Doctor though.

I think this may be it. I think she also probably feels at least a little bit intimidated by all he knows and has seen, and maybe thinks there's no way that someone like that could fall for a London shopgirl. Also, alien. Who knows if his people even work that way? She probably thinks there's not a snowball's chance in hell of anything ever happening, so she's trying very hard to pretend she's not even aware of him that way.

God, they're cute. Hee.