Rose Tyler is thoroughly confused and hasn't a clue what to do next.
She's not sure what to think, because right on the heels of losing the man she thought was the Doctor, she's had to deal with someone completely different all over again; this time, though, the face'd been the same. That had made for an interesting time of it, to say the least, and is the source for most (not all, but a sizeable majority) of her confusion.
All she knows for certain is that she has problems.
First off, she's kissed The Doctor (something she's wanted to do for a long time); as Cassandra, granted, but a kiss is a kiss in the end - and something hot curls low inside her when she remembers the feel of his lips beneath hers, the sensation of her fingers plunging through his hair and the expression on his face after it was all over. She's not sure, because she doesn't know this Doctor very well yet, but she'd almost say that he'd leaned in for and wanted that kiss; does that mean he wants her, too?
Add to that the fact that Cassandra, God love her, has just seen fit to announce to the world at large (well, to The Doctor, which is - at the same time - at least as bad as "the world at large", and worse) that she thought he was attractive - that she'd been looking at him in that way - and she doesn't know what to think; can't dare to believe that maybe, just maybe he feels something for her too.
She knows she needs to talk to him about it. She just doesn't know where to begin.