Century + old vampires and teenagers/young women... looks too much like pedophilia supernatural style.
Have you thought about writing a beloved as a mature human who lived a full life. Being fully claimed by her vampire mate would restore her youth but separate her from being reunited with her husband...
She isn't a twilight fan. The reality of feeding on people is hard to come to terms with. She is protective of her family though...
Will she entrust Him with the protection of her loved ones after her passing, or accept his gift of life and protect them herself?
There should be a lot you could do with the idea if you take your time with it.