Congratulations for your engagement,

Maybe, you can promises your fiancée that if she can wear the engagement ring every single day for the next 7 years, then you will upgrade her ring to a seven carat solitary diamond by then. Well, I am just kidding,

I think you can simply tell your fiancée what is the true meaning of the engagement ring, and the custom of engaged/married women wearing their engagement ring on the index finger of the left hand to indicate that they are no longer available.

Personally, I wear my wedding ring and engagement every day when I go out of the house, but I would take them off once I get home, And my hu*****and wears his wedding ring 24/7, even while he is sleeping