We have no idea why you feel you must save your daughter. If she and her fiance are good, hardworking people and they make decent money....why is it you feel the need to take care of them?
It is hard to figure out what is going on. But we dont have to know everything. For lack of information, I will assume you have no problems with your daughter or her fiance and that you just feel the need to finance their lives and take care of them, even though there is no need. If you are codependent for whatever reason, I have three suggestions.
1. Definitely buy and read Codependent No More by (I always spell this wrong) Melody Beattie. This is a great book. It started my journey to understsnding that I cant fix anyone but myself. Woke me up. I thought I had to fix everyone.. that this was my burden. This was especially true of my difficult child for much of his life.
2. Join Codependents Anonymous, a 12 Step group. This group was my main walk to better mental health. If there is not a CODA near you, or if you are shy, there are many online meetings. Sign up.
3. See a private therapist just for you. You cant stop old habits and guilt and the feeling that your adult child NEEDS you by yourself. You also probably will find the idea of putting your needs first very selfish at first...I know that I could barely wrap my mind around this. I thought it was almost a Cardinal sin to put my needs first. I needed to really work on that. I needed a therapist to straighten out my flawed thinking.
At any rate, those are the steps I took and I did eventually carve out a good life for myself. It took time, hard work and restraint.
I hope this helped.