Not zero, there was a recent case in the news of a woman killing both her parents and hiding the bodies for ages. There are others.
This is the one that posted 2 before yours.
There aren't any others.
Although in terms of elder abuse women, daughters, sisters have been identified as being equally likely as male relatives.
And although in the past if was thought more mothers were responsible for murdering their children, recent statistics seem to suggest this is no longer true.
Probably because of the increase in the number of Family Annihilators killings.