She and her husband arrived to adopt Lewis but were surprised that he was an inventor and were more surprised when Lewis introduced his newest invention. Learning that his invention was a Peanut Butter and Jelly Machine,she and her husband tried to leave but were too late and ended up being covered in P B & J, due to Lewis having failed to fix the machine. Alerted at her husband's state of condition, she yells at Lewis that "Mr. Harrington has a peanut allergy!" and runs to grab an epinephrine autoinjector to cure his anaphylaxic shock. She saves his life and then they turn to leave the orphanage for home. Despite Lewis's apologies, she said that it was nice talking to him and that they need some time to think about it and then slams peanut butter and jelly stained door. She and her husband walked into Mildred upon leaving, Mildred asks them what happened, seeing their condition. Mrs. Harrington angrily replies to Ms. Duffy that Lewis is not the right child for them. Mildred tries to convince them otherwise but they leave, slamming the doors to the orphanage, leaving Mildred devastated and Lewis hurt.
She's the only one who acknowledges that Mildred's last name is Duffy.