I’m sure that Frigga went to see Loki in his prison
with or without the permission of Odin. maybe they said:
"No Frigga he’s not the same Loki, he’s dangerous!"
"He’s my son..OUR son! you can’t stop me. we should go together to talk to him."
"Nope" *falls into the convenient OdinSleep *
( I dedicate this to the fucking awesome *megatruh :D )