Mrs. Sprat works as a nurse in the Knights of Malta Hospital special research wing and like the poem says, she is indeed fat. Mrs. Sprat is often regarded as a rather ugly and grumpy individual, which does her no good in a community filled with beautiful men and women. She is often nagging at Bigby Wolf for smoking inside the hospital. She was later seen complaining to Mayor Charming that he was behind in financing the hospital and was also invited to Snow and Bigby's wedding. Her husband was another of Ghost's victims.
In Fables #100, Snow White scolds her for her nasty, spiteful attitude towards Sheriff Beast and Beauty while the latter is going into labor. Snow explains that, while one can get away with being mean if she is beautiful, one can also get away with being hideous if she's pleasant, and since Mrs. Sprat is both ugly and mean she will have to do something about her attitude before someone has had enough of her. On the verge of tears, Mrs. Sprat reveals that she hates all the beautiful Fables, and became a nurse for the chance to have any of them under her care and at her mercy. When the Fables depart for Haven, Mrs. Sprat stays behind, unbeknownst to everyone else. Meeting up with Mister Dark, she offers to reveal the location of the other Fables for three things: to become beautiful, for all the other beautiful Fables to become ugly like her, and for a prince to love her with "true love". Mister Dark agrees to all three conditions, and the two depart together.
Mrs. Sprat is seen vaguely, most likely staying in Mister Dark's new castle in the Dark Lands. There, Mr. Dark shows Mrs. Sprat how to make herself beautiful by exercising and fighting her eating disorder by eating more lean and less fat. Mrs. Sprat is delighted with the great progress, but eventually becomes becomes impatient with her transformation and asks Mr. Dark to speed up the process, however painful it may be. While Mrs. Sprat is screaming and writhing in pain, Mr. Dark transforms her into an attractive young woman in a black dress. Mr. Dark then leaves to deal with the Fables, and promises to summon Mrs. Sprat to his side so that she will be there to see the beautiful Fables be made ugly before they die. He also plans to make her his bride and the mistress of Castle Dark, his fortress. However, Mr. Dark is killed by Mr. North, the North Wind, before any of his plans are carried through.
But this may not be the end of Mrs. Sprat's story or her vendetta against the "beautiful" Fables. And with her further lessons in fencing, it is possible that she could become a possible obstacle for Snow White and the rest of the "beautiful" ones. She is seen in Inherit the Wind arc, it is revealed that Mrs. Sprat's first name is Leigh. She now prefers to go by her maiden name Douglas, since the name Sprat is from a dead past. When Leigh's fellow Fables come to claim the castle as their own following Mr. Dark's death, Leigh dresses in rags and hides in a dungeon, pretending to have been Dark's prisoner, and claims that the reason for her slim figure is that Dark starved her. She also still has Werian Holt by her side, though what their plans are hasn't yet been told.
It is also possible Mrs. Sprat will appear in a future Fables' spinoff Fairest, she could be a possible antagonist for the story arc.