Anna Baker was the daughter of Sergeant Robert Baker.
Anna, Christina and Joshua Baker were all assigned to a different Vault than Robert, who went to Vault 51. He agreed to help the ZAX unit there in exchange for knowing that his family was safe in their Vault. However, in reality, all three of them died in an "accident" prior to the Vault's closure, and ZAX lied to Robert in order to gain his assistance. ZAX only let him know the truth as part of his last request.