Maybe the alien species died due because of many didn’t have the right immune system for fighting diseases. That Osira was the answer of making a hybrid. She could survive earth and their planet. That even if she did have a baby that the baby would be 50/50 due to how strong their genes are. So she is the only one. She winds up meeting the Banas but how should she be an enemy to Diana? Maybe because Gateway was actually her species doing ? That Osira’s coffin was put on display and she opens due to gateway’s power