As far as RPGs go, I would get her to play "Mario & Luigi: Partners in Time" first, since it's on the DS. GBA RPGs can come later, because even though she's into the gaming thing now, the way the GBA games stick out of the bottom of the DS lite may be a little turn-off for her.
Or you can just give her a GBA while wrenching your DS out of her hands and you'll be set, with all the games mentioned above.

If she can get into Final Fantasy Tactics, I'd suggest giving her Advance Wars before Fire Emblem. Fire Emblem frustrates me because the people die. However, since she's 'new', it might be a good idea to get her used to the idea of characters dying permanently to increase her strategical thinking. But then it might be stressful for her to have the painful ultimatum of continuing her quest after her Pegasus Knight is killed after spending an hour on a map, or restarting the whole thing and flushing the hour down the toilet.