She first appeared in Morty and Ferdie's 1932 debut strip, Mickey's Nephews, as a mouse lady arriving at Mickey's house and drops the twins off, asking if Mickey would not mind caring for them while she's running an errand. While in the original English version she had no first name and was referred to as "Mrs. Fieldmouse", a Dutch translation of the same of the comic strip had Mickey referring to her as "Amalia" (Dutch spelling of "Amelia"). In these original strips, Mrs. Fieldmouse is not Mickey's sister; as drawn, she looks more like an elderly relative, and Mickey refers to her "Mrs. Fieldmouse" rather than her first name. However, the relationship was changed to a siblinghood when she was re-introduced in more recent comics. The fact that Mickey is Morty and Ferdie's maternal uncle was also indirectly confirmed by the fact that, in the 1935Mickey Mouse one-pager He's a Knockout, Mickey states that he does not have a brother.
At Egmont Publishing, when her new design and characterization were fleshed out by Disney comic author Paul Halas and Disney comic artist Francisco Rodriguez, she was given the name Felicity Fieldmouse. As a side note, Egmont also named Felicity's husband—the twins' father—Frank, though he has yet to be specifically named or depicted in a published comic. Egmont's modern version of Felicity has slimmed down and is designed to look closer to Mickey in age while remaining significantly taller than him.
Mrs. Fieldmouse's early appearance as "Mrs. Fieldmouse".