INFO:

Firstly, how long did the two of you date prior to your engagement, and how much discussion did the two of you have regarding your eventual [undead] lives? Most relationship issues can be solved with clear and honest communication; whether to keep finances separate or combine them, whether or not to have/create offspring, whether to continue a monogamous relationship or allowing for additional vampire brides, etc, these topics should have been discussed thoroughly to determine whether your undead/life goals were truly compatible.

Secondly, what is the age gap between the two of you? Sometimes a marked difference in maturity levels can lead to conflict. Even amongst humans, May–December romances can be quite complicated due to generational differences, so I can only imagine the misunderstandings that must ensue in a 21st century–Pre Industrial era romance. With these generational difference there are oftentimes a great deal of misalignment in what each party assumes are "givens."

My advice would be to sit down and have an honest discussion now around relationship goals and how the two of you plan to spent either her remaining years or eternity together. Good luck.