My niece gave me a gift and I am going to refuse it.
Why would you do that to your niece?
She annoys me to no end. She also don't respect me.
Not accepting your niece's gift is petty. She went out of her way to get that for you, so you should just smile and accept it.
I don't have to do what she says.
You don't have to do anything that you don't want to do for the most part, but your niece would be very happy if you accepted the gift. You should just do it for her feelings.