Eppie is the least developed of the major characters, which is to be expected: hers is a functional role, and it hardly requires a fully characterized individual to fulfill it. During half the time she is in the story, she is a small child. There is no attempt to make her a special sort of child, except in Silas' eyes. She has the normal child's habits and a childish cuteness. This is sufficient for her function, which to that point is only to bring Silas into contact with his neighbors.
As a young woman, Eppie has a more difficult part. In order to show the sort of life Silas has achieved, it is necessary for Eppie to have some semblance of a personality. However, there is little time in which to achieve any complexity of character. Eliot takes some pains to give Eppie depth by showing incidents that are emblematic of her character rather than by providing a full background of her life. Thus Eppie's fondness for animals stands for all of her affectionate nature. She is put in the position of having to choose between her two "fathers," and this demonstrates that her affection has depth. A small touch of complexity is given by her wish to have one slight advantage over Aaron.
In the end, Eppie is most important for the effect her presence has on Silas' life and on Godfrey's. The character she is given is suited to her functional role, but it does not go far beyond that.