Queen Lillian makes her debut in Shrek 2. Although initially surprised at Fiona's transformation into an ogre, she is understanding of what has happened and, seeing that her daughter is deeply in love, accepts Shrek into their family. When King Harold is turned back into the Frog King at the end of the movie, she still accepts him as she did years ago. She and Harold are a reference to The Frog Prince.
In Shrek the Third, she is widowed and becomes a more determined character, leading the pack of princesses through a series of tunnels in the castle, and breaking two walls with her head, whilst humming "My Favorite Things" and "A Spoonful of Sugar" (songs originally sung by Julie Andrews in The Sound of Music and Mary Poppins respectively). She rallies the other princesses from being damsels in distress to independent fighters. It is revealed in the movie that Fiona inherited her fighting skills from her mother (Lillian asks "Well, you didn't think you got your fighting skills from your father, did you?"). After the film's finale, Lillian is seen in Shrek's swamp home, happily visiting her grandchildren and playing with Farkle, who vomited on her dress. At first, she looks distressed and a little disgusted, but this changes as she comes to find it adorable.
Lillian is seen briefly in a number of flashbacks, showing her and Harold's decision to visit Rumpelstiltskin to free Fiona from the curse before Shrek saved her. In the alternate universe, it is revealed she and Harold literally disappeared after signing over the kingdom to Rumpelstiltskin.
Lillian's last appearance is at the end of the film, seen celebrating the triplets' birthday.