Lucy (Born Around 2003 and 2004) is the only daughter of Janet. She is considered by her mother to be a "miracle baby" because Lucy was born from the only good egg she had.
She is supposedly "very gifted", but it is unclear whether it's true or just her mother praising her only child. She's known to have anger management problems and pushes her mother around.
Brick is not very fond of her. Brick has said "For a miracle baby she's not so bright." She is known to be with Mr. Bear.
In season 2, Lucy did not make an appearance, but Pat and Spence went to Janet's for thanksgiving again because they didn't want to miss Lucy's ballet recital. This caused a lot of arguing between Frankie and her mother and sister.
In season 3, Lucy made her first appearance when Janet, Gary, Lucy, and the Hecks went to Pat and Tag's for thanksgiving. Janet, Gary, and Lucy got the big bedroom because Janet thought it would be better for Lucy to have her naps than in the living room on the sofa. Lucy at first continued to bother Sue to play with her, but Sue ended up passing Lucy onto Brick to play with. Lucy and Brick do not get on, as Brick keeps winning all the games causing Lucy to get upset. When Brick and Lucy went outside to build a snowman, Lucy lost her favorite toy, "Mr. Bear". Which caused everyone to go outside in the snow to look for him. Axl found him but he was broken as he was in the snow and was all wet, and caused his voice not to work anymore. Lucy blamed Brick saying that he had him last.
In season 4 when Janet came to the Heck house to help out Frankie while she was studying for her dental exams, Janet told Frankie that the main reason why she came was that she needed Frankie's support as Lucy had become aggressive and violent and turning out bad (really, really bad). And the only time she gets a break from Lucy is when she (Lucy) holds her breath and passes out. Janet also said that she screams and throws her toys at her and then pulls up her sleeve to show Frankie what she did to Janet for just being asked if she wanted a bath. Janet also said that she and Gary sent her off to a fix-it camp called Camp Tantarum, meaning tantrum. And Janet was scared for when Lucy would come home as she'd be so angry with her parents.
In season 5 Janet asked Mike and Frankie to house sit for them while they took Lucy to a "How to Tame Your Violent Kid" session.