Remember, if it is a decoration of any type that you do not want broken, I would consider not putting it out for a few years until your children are a little older. Takes away the stress for everybody, and congratulations, btw, that is a wonderful blessing. Think win win with the tree and everything else. I imagine you are tired right now anyway, go for the traditions but not if doing them is going to exhaust you. If you bake cookies, for example, do it but maybe just the chocolate chips instead of the five different cookies.
This may sound stupid but just teach her not to. My daughter amazed a woman at that age because she went to her house at Christmas and got right up to things to look at them but didn't touch. I taught her not to by being right there with her and stressing how important it was to look and not touch the pretty things. One of the decoratons we have are these boxes, they open one by one and the little characters twirl around with a different xmas carol for each box. My daughter would sit there and clap while they twirled and when the box started to close she would wave goodbye.
She enjoyed it immensely without "trying" to destroy it. I would show her all of our different musical snow globes but I would let her know that mommy had to wind it up so we didn't break the pretty things. Thank God she wasn't a boy, they look at things and they break. I don't remember how we managed the boys, probably daughter helped me by playing watchdog while they were small (they are now 9, 13, and 16 and I have slept since then).
Just keep telling her over and over again not to touch, it is dangerous and can fall on her and not to touch, because it is pretty and we don't want to break it. I would recommend buying non-breakable ornaments if you don't know if she can do this and if you are like me and have ornaments from my own childhood that are breakable.
Ironically, the kids wanted a dog a couple of years ago, she is huge, 110 lbs, and she would take out a tree in a nanosecond with her tail. I still haven't figured out the xmas tree question with her because I have so many breakable ornaments and had a tree incident 13 years ago when we moved; I was lucky because what did break had no sentimental value.
The little kid, seems like a total nightmare but let her see things as you put them out, don't try to do the tree when she is asleep or gone, have someone to manage her while you do stuff and then the curiosity factor is not quite so big.