I don’t see that there needs to be a separation between being nice and being angry if my other choice is being mean.
I was told by a 5-Elements TCM practitioner that anger is viewed as the energy necessary for growth, what cracks the seed and pushes the infant plant up to daylight. But anger has to be in balance. Excess anger and lack of anger are equally detrimental to health.
I saw a lot of women with their children, from babies through teens. I think they set a good example of how anger and, yes, grief can be channeled into meaningful action.