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

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1. I think it's great that you're focused on your relationship with her and thinking about it.

But it does seem a bit over-the-top for your niece to be so very angry about your forgetting her birthday. I could see her being annoyed, and maybe having her feelings hurt a little, but a friendly sincere apology from you along with the belated birthday present ought to be able to clear the air.

My advice is to gently express your apology, to tell her how much her friendship means to you, to give her the present, and go from there. If she accepts this, you could take her out for a casual meal or treat of some sort. If she doesn't accept it, she's going to have to take some time to figure out some other way to deal with disappointments.