Our 1 1/2 year old Chiweenie likes to try to take the ornaments off the tree, so we have to watch her all the time. If we can't watch her, she's goes in her crate. Make sure you watch her, but don't anticipate problems. Act like she's not gonna be naughty, and if she is might just ignore the tree. If she does try to go after the tree, claim the tree by standing in front of it, between the dog and the tree, with your shoulders back, chest up, and a positive attitude until she backs away and ignores it. You can also tell, not yell at, her, "No, my tree." Since dogs don't really understand speech, this is more for your benefit to help with the energy you're sending the dog. If the dog tries to go around you to get to the tree, move so you're still in between her and the tree.