J, she's your sister. Buy her something that is not a gift card.
i used to go all out on presents for her when i was a kid, but we've been at war since Christmas 2001, the year she borrowed my boom box, brought it to swim practice, got it wet, ruined it, and then got me a new boom box (only worse) for Christmas later the same year.
i opened it and said, "thanks for replacing my boom box, now where's my present?"