Lilly is the main protagonist of the "Really You" episodes.
At first,she was an overindulged tween who usually got what she wanted,since she was the youngest,and she had a "gift" for manipulating her dad.
Her mother was often frustrated by her actions,as was her brother,as her brother felt she was in need of self control.
All this changed when "Lilly D." (one might surmise the "D" was short for Deluxe) a life sized "Really You" doll,was purchased for the precocious tween. At first,Lilly was no better than she had been previously.
Then,odd things began to happen. Random "accidents" which Lilly tried to blame on Lilly D.,as Lilly was told by another girl who had been invited to Lilly's house,that "Lilly D. hated her."
Her mother dismissed the claims as being "rubbish",scolding Lilly in the process. Her brother however,began to suspect that "Lilly D." was trying to replace Lilly.
Eventually,her brother learned the truth behind "Lilly D." She was trying to replace her "human doppleganger",as Lilly D. was "evil and she wanted to be human",according to the dollmaker who knew the truth about "Lilly D.",but was ignored.
After a trip to the doctor,as Lilly had fallen ill,for no apparent reason,"Lilly D." revealed to Lilly she was alive,by smashing a vanity table mirror. Lilly's mother didn't listen to her daughter,instead saying "I wish Lilly D. was my daughter,instead of you",before entering the bathroom for a few moments of relaxation.
Lilly and Lilly D. then swapped places,with no one the wiser. The now human Lilly D. went on to explain she was "after her mother's love."
The "new Lilly" seemed to be a total reversal of the "old Lilly." She was sickeningly sweet,and polite. During dinner that evening,she was praised for her new,unselfish behavior. Unseen by the family,the "real Lilly shed a single tear",which the "faux Lilly" wiped away,before anyone could see that her "mother" upset "the doll."
"Lilly" dismissed her father's suggestion that some new "accessories for Lilly D." were in order,by saying that she was "over dolls." After dinner "Lilly" took "Lilly D." out to the trash container,to remove her from the picture. As "Lilly D." awaited the garbage truck the next day,"Lilly" told her "its good to be you." As an afterthought "Lilly" told the real Lilly,"I always hated you."
However,Lilly D's scheme was undone,as he brother discovered the switch. Imploring his mother to not let "Lilly D. be taken by the garbagemen",he gave chase to his "sister",as Lilly's mother discovered the truth as well;"Lilly D. was really Lilly." Lilly and her "doll doppleganger" were restored to their rightful bodies soon after. The episode closes with "Lilly D." being found by two girls who bicker over who will get the doll. The girls run away in terror as Lilly D. grabs one of their ankles,indicating she is still very much "alive."