My gosh!
only about a few weeks ago, it was impossible to handle her, now, she's exploring all over you and your fiancé
She's very small, it's been ages since I've seen a young syrian hamster. They are so tricky to handle when they're young because they can run at an incredible speed
You've managed to control her behavior gracefully (doesn't sound like she had bitten you today!) I've seen all too well hamster's becoming increasingly aggressive and stubborn to tame. Handling them would be out of the question! If your hamster is untamed, it doesn't mean that they aren't happy, and enjoying life, it just means you cant have any physical contact without a bloody finger :P
As far as you and I can see, Nibbles definitely wont be going down that road
I bet in another few days or a week, Nibbles would have passed her 'Taming course
' and will be friendly for life!