All you can do is sue her for the value of the item in small claims court. If you can convince the court by a "preponderance of the evidence" (that is, that it is more likely than not) that this was your item, the court can order her to you its value. However, if you don't have any documentary or photorgraphic evidence (e.g. purchase receipt; photograph of you with the item; etc.) so it remains your word vs. hers, you are unlikely to win: as the person suing, the burden of proof is on you, which means that if the court cannot tell who is telling the truth, the defendant (the other person) wins.