They were actively worried that she would commit suicide.
They had to hide the knives from her.
I'm sorry but I would not leave my children alone with anyone that I thought might commit suicide.
I might not think she's going to murder her own children. However, I wouldn't want my children to see their own mother killed, and then I wouldn't want my children to be unattended.
Your new information changes my opinion.
Even if she was only a danger to herself, she should not have been left alone.