So... she wants you to choose for her? Well... fair enough, then, I guess.
Shameless and pointless necroquote, but I found this hilarious.
Anyway, I would recommend you start as her being a sorc and you being a warrior, or vice versa. I find Korriban to be, by far, the easiest and least annoying starting planet, and I think if she gets bored early, she'll be much more likely to not want to play. If she isn't annoyed right away, she might get more sucked in. Although you'll have to pick your server wisely, because some of the Korriban general chats are the most wretched of wretched hives of scum and villainy.