Why would a girl want to keep an engagement ring even after a divorce?

This happens quite frequently that the girl wants to keep the engagement ring even after the divorce. In my case, my ex is the one who wanted the divorce, but she also kept the engagement ring. Why would you want to keep an engagement ring if you didn't even want to stay married? It seems to me more like greed and/or spite.
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Girl: Remember that ring that I accepted as a condition of love and marriage? Well I've changed my mind. I don't love you and I want a divorce. But I'm going to keep that expensive ring anyway
Why would a girl want to keep an engagement ring even after a divorce?
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