Freyja isn't the only goddess out there with a twin brother. And having a twin bro isn't always easy, even when he's as cool as Frey. Sometimes you need to vent to other goddess like you.
Like Freyja, Artemis is a twin sister to the male god of light, Apollo, and is a goddess of fertility. Though Freyja and Artemis bond over having twin brothers, they can't be BFFs because Artemis is a virgin and has spawned an army of virgin nymph imitators, whereas Freyja is the most promiscuous of the Norse goddesses.
Artemis may be cool, but Freyja and the Aztec goddess Xochiquetzal just click. They're both in the part of the Prom Queen clique, plus Xochiquetzal is also a twin – to Xochipilli, god of art, music, and games.