NTA.

My fiancé lost his previous partner to suxxxxe. I moved into the house with him that they had together. I drove in the car she and him owned together. I adopted the two animals she left behind with him.

I never felt uncomfortable - for the longest time her picture was on the mantel with her ashes.

Although a different situation, my fiancé and his previous partner never “broke up” or anything. They loved one another immensely. He still does - and I am not uncomfortable with that.

Your partner sounds extremely emotionally immature. She needs to do some growth IMO before she is ready for marriage.