We don't really know a whole lot about Sophronia Lammle apart from the fact that she's a schemer who grows a conscience… and then returns to being a schemer again. We first learn about her when she has married Alfred Lammle and is disappointed to learn that he has no money. Alfred is equally disappointed, because Mr. Veneering has led both of the Lammles to think that the other one is rich.
As we learn from the book, Sophronia's initial reaction to her marriage with Alfred is not good at all:
Then she cries again. Then she is enraged again, and makes some mention of swindlers. Finally, she sits down crying on a block of stone, and is in all the known and unknown humours of her sex at once. (3.7.91)
But later in the book, she develops such a love for Georgiana Podsnap that she can't let her husband carry out their scheme of marrying Georgiana to Mr. Fledgeby. Sophronia ends the book in a half-redeemed state, since she has at least done the right thing in saving Georgiana. But it still looks like she'll carry on a scheming future with her hubby Alfred.