You know everyone shows grief in a different way, even though you feel they were not close, i am sure she still feels something now he is gone, i do believe from what you have said she has always been that way,not doing anything to help,if she is depressed though even lifting a finger can be mamoth task, however you and you alone only know your niece, so i feel you are the only one who can set the rules,i would imagine she needs rules just like anyone else, if she is not used to that way of living, well she will get used to it in time, if i were you i would not be too hard on her right now, give her a chance to one get used to her new surroundings and two deal with the loss of her father, whatever her relationship was with him, i have no doubt she will be feeling some sort of loss.

It is obvious you love her, or why would you even bother to take her in and come here to vent, it is good you have a place here to do just that, hopefully some of our suggestions and opinions may help, hope so, take care and all the best.