I figured it's not harmful because they are in the wild but I just wanted to check. She doesn't seem to be eating the tree, she just goes under it and seems to be smelling it and chining it. I just want to be comfortable walking away from her while she is under there knowing that if she eats it she won't get sick.
You do realise that all poisonous plants grow in the wild, don't you? ^^ Wild rabbits seldom poison themselves, not because there are no poisonous plants but because they've got some group knowledge of what to eat in their natural environment. When you move them, they don't know anymore and can poison themselves. Our rabbits have zero instincts about what to eat or not. Fir is not poisonous in itself, but the trees you buy for Christmas can contain insecticides, paint, fertilizer, preservatives... so it's best if your rabbit don't eat it even if it's doubtful he'll drop dead from a nibble (don't put any false snow where he can reach). You'll have to watch him, because some rabbits really like the smell of fir. Just in case: holly and mistletoe are both poisonous so beware!
Don't put tinsel or fragile bubble where your rabbit can reach. You can put harmless decorations at the bottom of the tree (there are tissue decorations or some done with ratten, or I've seen some done with dried pieces of orange...)
You mention light cords. I'm warning you those are the first cause of death for rabbits and most rabbits have a hard time resisting them (mine certainly couldn't, thread like things put them in a transe). I personally wouldn't risk it.