Supergirl comes to help as Maggie and Alex are chasing down a truckfull of thieves with heavy weaponry in episode 3x01 "Girl of Steel".
Everyone arrives in Central City for the wedding in episode 3x08 "Crisis on Earth-X, Part 1".
Kiera rides drives with Garza while talking to Alec and heading to the warehouse in episode 4x03 "Power Hour".