My thoughts: you said you forgot she had it thinking you lost it on your own. So at that point I assume you'd moved on. I think you should assess what is fueling such emotion right now. Is it that you now realize it's still out there and you didn't lose it so you feel the attachment? Or is it that it hurts you that she has your sentimental piece and you don't? If you were able to detach from it when you thought you had lost it, you should try to detach from it again and move on because she's being malicious. Yes she is probably busy and might not be intending to be malicious but she is by knowing she has something that belongs to you that you want back and by brushing it off. If you're missing the item because you realize it's still out there and not because she has it and you don't, then I'd text her often. Just come out and tell her you consider it theft at this point since she knowingly has something that belongs to you and that you have asked for repeatedly. And tell her if she doesn't get it back to you by a certain date you'll file a police report. Others say it isn't theft because you lent it out but yes it is still theft. If someone lends you something it doesn't belong to you, when they want it back you are obligated to give it back. If you don't it is theft. If a bank lends you money and you say you don't need to give it back when they want it, it is considered theft and fraud and they can come after you for recourse. Same thing.
Put the same pressure and stress on her that she has on you. File the report. Beat her at her own game and let her deal with that stress. I bet she will come up with it quickly so she can focus on her exams.
