My sister is trying to claim something very important to me as her own, and it's not, not sure what to do?

My sister is convinced the bonnet I wore for baptism is her's. She wants it to make a wedding handkerchief out of. It is not her's, it is mine. I was 7 when she was born and I remember very specifically what happened to her's. Her husband had an affair at the time (my sister'sfather, not mine) and my mother destroyed the things that were keepsakes that were my sister's because she was going to ditch her with him and she wanted everything important to him and my sister destroyed. Anyway, they got back together and now they are both deceased. I don't want to tell my sister what happened. But I don't want to give up my bonnet to be cut up when it has nothing to do with her. My daughter has already worn it and I want all my kids to wear it. I don't know if I should tell her the truth to back her off or what. She is getting very nasty about it.