You don't want to have to go back to the jeweler for a resizing if you can help it...ideally the ring will slide right onto her finger and stay there as a symbol of your love! But how can you find out what size ring she wears, without making her suspicious?
Sneak into her jewelry box and do one of the following:
• Make an impression of one of her rings in a piece of clay or other
moldable material.
• Trace the inside of the ring onto a piece of paper.
• Take one (only if she will not notice!) to the jewelry store with you.
If your fiance-to-be is not in the habit of leaving jewelry where you can have easy access to it, ask one of her friends or a member of her family to try to get the information out of her. It's amazing what girls talk about with one another without the slightest suspicion!