Cluelss forgetful uncle needs help getting back on his niece's goodside. Need womanly advice.

[De Leonist]

So I forgot my niece's birthday, she turned 10 this month. She is now very, very upset with me Perhaps this is small potatoes but here is the thing. I'm wrapped around my nieces' fingers, and they know it. Nuclear War could decimate the world. Cthulu could return to devour the souls of all humankind. Arby's could stop serving curly fries. All these horrid, horrid events could take place and yet none of them seems as horrible as the fact that one of my nieces no longer considers me her favorite uncle. I don't honestly know how to fix this. So please oh gentle, fair, kind and wise women of DU help this poor, clueless, creature before you with suggestions for quelling a 10 year old girl's anger.