That bothered me at first, too, but it was explained in the first episode of this season, thankfully!
She didn’t realize Bonaparte was dead until Sean told her about it later, and then she was afraid to take it off because the ring itself was cursed, not just laden with a threat from Bonaparte.
She’s afraid the curse may not be gone just because he is, and wants to make sure nothing will happen to her children before she takes it off and risks their safety.