This weekend during Cartoon Network's DC Nation block, Supergirl will have to deal with being grounded. No, she's not walking across America, just being kept at home under the orders of a certain Cousin of Steel for misbehaving. When her super best friends Wonder Girl and Batgirl arrive seeking her aide in a battle against evil, however, the young heroine can't resist lending a hand. Too bad her only living relative is impossibly good at enforcing rules. See a clip from this weekend's Super Best Friends Forever short, "Grounded," after the jump.