One of the problems some clients face is that they have a slim finger, but a large knuckle. This may be due to swelling, or an injury, or maybe it is just the shape of their hand. At any rate, it presents a problem.
If the case is mild, the best thing to do is choose the smallest ring size, which will go over the knuckle without making the person feel uncomfortable after it is in place. It may help to us hand cream to alleviate inflammation. Assuming there is not any discomfort or tightness on the finger, the 1-carat solitaire round diamond ring will stay in place.
As for wearing it on the big day, you can set your mind at ease by applying hand cream to the finger with the ring on it. The finger will get moisturized, and the ring can glide on faster, and more easily.