This isn't something that I have encountered personally, because I don't own the Life & Death expansion, but noticed when looking at the quotes on The Sims Wiki.
Esther Gomes' pronouns are xie/xem/xir/xirs/xirself. However, when xir sister (Tziporah Gomes) talks about xem, she uses xir pronouns incorrectly:
All the friction I have with Esther is so frustrating for me. I just want xir to understand why it’s so important for xir to live again. Xie thinks being dead is fine, and that the abilities xie has make it even better, but I can’t accept it. Because I can write, I decided that I would work towards being able to write a Book of Life. When I have one, I’ll be able to convince xir to come back. I know it. Esther will understand someday.
The use of "xir" in every instance here is incorrect, and should be "xem" because that is the object pronoun. If corrected, it should say this:
All the friction I have with Esther is so frustrating for me. I just want xem to understand why it’s so important for xem to live again. Xie thinks being dead is fine, and that the abilities xie has make it even better, but I can’t accept it. Because I can write, I decided that I would work towards being able to write a Book of Life. When I have one, I’ll be able to convince xem to come back. I know it. Esther will understand someday.