I have heard, and choose to believe, that heaven will have everything that makes us happy. Since I believe I will be happy to have the presence of my beloved pets with me in heaven, I KNOW that pets are allowed there!
I will pray for you, your wife, and your beloved kitty. Heaven open it's gates for her, and God's arms comfort you and yours when the time comes for kitty to go home. I will pray that kitty doesn't suffer pain, and that when her time comes, she knows your family loves her and that you give her your blessing to pass so she doesn't suffer any anxiety in making the transition.
Bless you all for loving her so much.
My Mom was always terrified that her favorite dog would die before her, so we planned that if he did, we would go right away to the animal shelter and adopt a puppy. Going from something to complete nothing is so hard.
Perhaps you could consider this too. It wouldn't be the same cat, but at least could help a bit.
Blessings to you.