Is the questioner wrong in her inability to receive her former husband's brother's wife, due to her feeling of harm, and what should she and her husband do in this situation?

We do not say that you erred, but rather that you acted contrary to what was preferable. Marital problems are normal occurrences. You and your husband must live together in kindness and strive to preserve the family unit, being wary of anything that could lead to its destruction, for Iblis is keen on separating loved ones. Your husband and his family have no right to accuse you of having a black heart. You should forget what happened and deal with your in-laws naturally. It may be that the separation of the man from your sister is better for both of them, for Allah, the Exalted, says: "But if they separate [by divorce], Allah will enrich each of them from His abundance. And ever is Allah all-Encompassing and Wise." [Quran 4:130]. And whether or not there are children has no effect on enjoyment.