Judging by the stem size, color, leaf scars, the tiny little nubs that are leaf buds, etc, I'd guess some sort of dieffenbachia. Of course, no idea what kind of variety until you have leaves. The stems are normally straight, but when they get overgrown in lower light situations, they can bend into some weird shapes. This won't damage it at all, just will make potting it up a little interesting.
Assuming it is dieffenbachia, you can root it in water like your sis said or you can root it directly in a pot of soil. These guys root easily. Once it roots and you pot it, keep it slightly moist to slightly dry - they are really easy to grow, they just don't like to have "wet feet" or they'll rot.
Oh, edited to add: Diffs aren't vines, they are more shrubby (tho, I don't know if they are technically considered shrubs, per se).
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