Before the First Curse
Milah is introduced as the wife of Rumplestiltskin. Before Rumplestiltskin went to the ogre war, Milah is shown to be a devoted and loving wife to her husband. When she is first seen, she is doing some mending when Rumplestiltskin comes to their home to announce that he is going to the front line. Milah is thrilled for her husband, and tells him to go to the front and fight.
Several months later, Milah gives birth to their son, and shortly after his birth, Rumplestiltskin returns home. At his arrival, Milah at first appears happy to see him, but then asks Rumplestiltskin if it is true that he injured himself to return home. When he asks where she heard this, Milah tells him she heard it in the village. She then calls Rumplestiltskin a coward, and that it would have been better for him to fight and die on the battlefield rather than return home to her and sentence his son to the life he will lead. She thrusts Baelfire into his arms, and storms out of the cottage, slamming the door behind her.
Several years later, she is seen in a tavern drinking and enjoying herself alongside Hook, back then known as Killian Jones, and his crew. When Rumplestiltskin comes to retrieve Milah, she rebukes him, saying for him to go to home. It is only upon the appearance of her son, Baelfire, that she goes home with him and Rumplestiltskin. Later, as she lays in bed, she expresses to Rumplestiltskin her displeasure with her current lot in life. Milah wishes that they'd leave this village life and go explore and see the rest of the world. Rumplestiltskin asks her to try if not for his sake, for the sake of their son. She agrees reluctantly. The next day though, she is supposedly kidnapped by Jones' crew and taken away when Rumplestiltskin will not fight for her.
Years later, after Baelfire's disappearance and Rumplestiltskin's transformation into the Dark One, he tracks Jones down with the help of William Smee, an acquaintance of Jones. Smee is in possession of a magic bean, and says he will give it to Rumplestiltskin in exchange for eternal life. Milah appears again in an alley in the middle of a sword fight between Jones and Rumplestiltskin, after he has been told by Jones that she died years earlier. She tells Rumplestiltskin that the night she was in the tavern with Jones and his crew, she fell in love with Jones and the pirate life he described to her. She made the decision to join his crew. Milah reveals Smee's red hat to be in her possession, and tells Rumplestiltskin she will give him the magic bean in exchange for the life of herself and Jones. Rumplestiltskin agrees.
On board Jones' ship, Rumplestiltskin appears and Milah asks if the deal still stands. Rumplestiltskin appears to agree, then asks Milah if she thought about her son Baelfire when she left. Milah retorts that she has lived with the regret of leaving her son behind for all this time, but that she could not see through her misery in their marriage to think about him. Asking where this misery came from, she firmly states is because she never loved him. In a fit of rage, Rumplestiltskin responds by driving his hand into Milah's chest, ripping out her heart as Jones watches helplessly. He rushes to Milah's side, only to have her die in his arms, saying she loves him, as the woman's heart is crushed to dust by Rumplestiltskin. He later cuts off Jones' hand that he believes contains the magic bean. Milah's body is dumped overboard moments before Jones, now Captain Hook, sets sail for Neverland through the portal the magic bean created when he threw it into the water, vowing to avenge his love's murder by her ex-husband.
After the Third Curse
In the Underworld, Mr. Gold encounters Milah as a crossing guard and enlists her to help him and Emma rescue Captain Hook from his prison near the River of Lost Souls. She is shocked the blonde has been in relationships with both Killian and her son (the latter she had a child). After helping them make it past a barrier, Milah is told by her former daughter-in-law that Baelfire had passed on to a better place in death. While waiting for Emma's return, she admits to Mr. Gold that her guilt over leaving Baelfire is keeping her in the Underworld; regretting how she treated their son poorly just because she grew to loathe his father. Recalling Baelfire forgiving him for leaving him, Gold assures her their son will do the same with her as well. Since she now knows Baelfire is now happy and in a better place, she has hopes her unfinished business is done, and that she can move on, with Gold asking her to give Bae his regards. Milah is temporarily frozen by Hades so that he can make a deal with Mr. Gold. After the discussion, Mr. Gold was forced to destroy the boat. Then Mr. Gold regrettably sends Milah into the River of Lost Souls all the while feeling remorse. When Emma and Captain Hook arrived, Mr. Gold told them that Hades attacked and sent Milah into the River of Lost Souls by deflecting his magic.
Fortunately, this possibly isn't permanent as Hook and Arthur theorize with Hades' departure (and demise), the condemned souls, including Milah, can be freed from their fates.