Aunt Em is given a full name on the show, Emily Brown. she is played by Gina Stockdale, and appears in the Season 5 episode "Ruby Slippers".
Before the First Curse
After Dorothy returns from Oz, Emily is the only one who believes Dorothy about her travels to the magical land, as the rest of the family tried to have Dorothy committed. Emily then gives Toto to Dorothy as a gift and dies soon after.
After the Third Curse
After Emily dies, she is sent to the Underworld, where she runs a diner. She is rivals with the Blind Witch, who is her business competition.
After the heroes discover Dorothy is under a sleeping curse, placed on her by Zelena, they try to find ways to get back to Oz to save her. Ruby reveals that Aunt Em was the only family member Dorothy ever loved, as the rest of her family was awful to her. Emma suggests searching for Aunt Em, as she might be in the Underworld.
The heroes go to the Blind Witch's diner asking her if they know anything about Aunt Em. The Blind Witch reveals her hatred for Aunt Em and tells them where to find Em's diner. Aunt Em greets them at the diner, and Emma tells her they are trying to help Dorothy, as she needs True Love's Kiss to wake her from the sleeping curse. She asks Aunt Em to blow a kiss into a bottle. However, after Em takes the bottle, she melts into a puddle. Shocked, the heroes question what happened, and Hades reveals himself, explaining that he laced her soup with water from the River of Lost Souls. He wipes her up with a dishrag and drains her into a jar. Because of this, her headstone in the Underworld cemetery becomes cracked, indicating she's gone to a worse place. Hades later empties her into the River with the rest of the lost souls.