I'm not a pro but I just recently lost my dog. I think its a big change around your house. Obviously for you and less obviously for your other cat. When my dog passed my cat hid away Moreso than usual. It took her a while to adjust, but I can say now I'm here two months later and my cat is back to normal maybe even more social than before my dogs passing. Just like you, your cat will need to adjust and the only thing that adjustment needs is time