Aldrif Odinsdottir (Angela) was the first born of Odin and Freyja, and heir to the Asgardian throne. When Heven waged war on Asgard, the Queen of Angels kidnapped Aldrif in an attempt to blackmail Odin into surrendering. He refused, and the Queen seemingly killed Aldrif before fleeing.
Following this event, Odin used his powers to cut Heven from the other Nine Realms and Yggdrasil.
After the Queen of Angels ordered the corpse of the baby to be disposed, the Angel tasked to do so discovered it was still alive, and raised her as one of the Angels under the name of Angela.
After the Orb releases the Eye into the Avengers, Thor sees that Angela is Odin's daughter, and therefore his half sister and the foster sister of Loki, discovering Angela's heritage, Thor heads back to Asgardia to ask more about Angela from Freyja. After learning a few more details, he heads with Loki to Heven in order to learn more about their lost sister.
Odin, who had been liberated by Loki from his self-exile in old Asgard, recognized Aldrif Odinsdottir as his daughter, and offered her to join him and the rest of the Asgardians, Angela refused, as she was raised to think Asgardians were her enemies, but couldn't stay in Heven due to the Angels rejecting her for her lineage.
Odin and Freyja had another child (unnamed baby girl and Angela sister). Angela went to Asgardia and stole her, and left Asgardia. Her motivations are unknown but she has Sera an Angel "friend" help, Thor Odinson, Sif and the Warriors Three, were send by Odin to retrieve the child and punish Angela...
Angela Asgard's Assassin Discussion...by Kieron Gillen, Marguerite Bennett, Phil Jimenez and Stephanie Hans...