My youngest daughter suffers from the same thing. She has days where she not only lacks empathy, but basically any feelings at all. It has taken years but I think our family has finally adapted and learned how to react with care even when she blindly lashes out about how everyone around her is so emotional when something bad happens in the news etc.
I definitely spent a lot of time in her shoes. It took a long time for me to be able to suss out how my words might impact others, and why someone might be reacting how they are. But it does get better. It takes patience and lots of practice but it's definitely doable if she's willing to put in the work.
And also good on you for responding with care and love. That is so hard to do, but god it matters and helps so much. You're an incredible person and parent for choosing that path.