I really enjoyed reading about how much fun you are having with your horse. I think it is good to allow the horse to smell and be curious about things, but I am a little concerned about just a couple of things you mentioned. What you need to remember is behavior in horses is like rolling a snowball- it starts out small and manageable at first, but will always get bigger. That is why some believe what she is doing is a precursor to biting. This type of behavior happens a lot in the herd, with young horses becoming more aggressive with the older ones- it starts with just a little nudge or push and then progresses.
Secondly- I would be concerned about her becoming a little spooky under saddle. While it maybe manageable now, if something happens out of the ordinary, you may not have enough control to keep safe.
Let her be curious, but insist she keeps her distance. Allow her to come close but only after you have given her a signal to come in (maybe a cluck) and make sure that she stops immediately, any time you give her the stop command. Whether you are leading her, handling, or riding. Stop is without compromise!
Enjoy your horse and keep safe!