1)她先把自己家的钥匙留给你们的。If she stole from you, she would suspect you would do the same and asked her key back.
2) Even though you do not wear those gold jewelry, it does not mean you do not check it every other day. And she does not know that. So, no reason for her only steal those jewelry, not cash or other stuff.
3) If she stole, she would do anything to keep a normal relationship. Apparently, she is also busy with other things now and you are not top priority. (Or maybe, you hinted something and she is not comfortable with it.)
I would suggest you check your family members first.