Myths in which Freya appears: (under construction)
Thor’s hammer is stolen. Loki finds out that the jotun Thrym has it, and will only give it back if Freya becomes his bride. Thor tells Freya to get dressed in her bridal gown and go with him to Jotunheim to make the exchange. Freya gets so enraged at this that her necklace (likely Brisingamen) breaks and and the walls shake with her fury. The Gods don’t know what to do, and they call an all-gods meeting in Asgard. Heimdal suggests that Thor dress up as Freya and go to Jotunheim pretending to be her. Thor is offended at this suggestion, saying that all of the Gods would make fun of him if he does this. Loki assures him that all will be well, and that he’ll come with as Thor’s bridesmaid. Thor makes a odd-looking bride with glowing, fiery eyes and a huge appetite, but Loki explains it all and Thrym buys his explanation. Finally the hammer is put on Thor’s lap–as it would be put on any bride’s lap during a wedding–at which point the jig is up, and Thor smashes every jotun in sight.
English translation of the full text of this myth available here.