This is Dr. Cynthia. Thank you for contacting us. I will try to help with your concerns.
Thank you for the description of your issue.
Is your question about the cats accepting each other, or about Shadow's hostility in general?
Shadow is unlikely to ever accept the other cat.
The Savannah is going to be a lifelong challenge. Not just for Shadow, but for all of you.
And I do know cats.
If you are going to keep the Savannah, which I would suggest you not, you should provide Shadow a safe place of her own. Any room or area where she tends to spend most of her time. Keep her food, water, and litterbox in that room, and keep the other cat out.
When the cats have access to the common areas do not force interaction. I would imagine Shadow will retreat to her "safe" place.
Let me know if you have other questions.
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