lol I mean I am gonna make it official one day. Just not this month
Dont listen to the idiots who think its dumb to take it slow.
But if I understand correctly, she is the girl your interested in, but you just want to take it slow and ease on into a relationship.
Now you said you like to talk to her alot. I assume you just go hang out with her and just talk as your hanging out.
What I would do is just go hang out at the usual place, or take her to get a bite to eat or something(a casual place, not neccesarily a resturaunt), and then just ask her to close her eyes for a second.
Then you put the necklace on her, and then you tell her she can open her eyes, and you say Merry Christmas.
Alternatively you could wrap it up, and just tell her "this is for you, Merry Christmas". And then she opens it.
A other alternative, is you could wait till you are ready to enter a relationship with her, and give her the necklace then. And get her something else for Christmas.
The main thing though I would think, is to give it to her in a casual place. If you take her to a more formal place, then it would have the possibility of giveing her a bit of mixed signals.
I got one final idea for what you could do. Im not sure if she would like something like this, but you could make a small game, where the end result is the necklace. For example. You could make some notes that lead her to several different locations, and then the end location, would be her mailbox, where the necklace would be wrapped.
Ex. Note on her door "go to the starbucks and look under the table in the corner"
That note says "go to 1st street, and look on the 2nd telephone pole past the main street intersection."
That note says " go check your rear tail light"
That note says" go check your mailbox"
Then you could have 1 of 2 things. 1. Turn around(then you give her the necklace) or 2. Open this(then she opens the wrapping, and the necklace is there. Then you come up from nearby her and tell her "Merry Christmas."
These are just some ideas that i thought of off the top of my head, not knowing anything about the girl.
Ultimately though, it is completely up to you. If you do what you feel is right, then im sure you will be fine.
I wish you good luck, and hope you have a Merry Christmas and a Happy New Year!