More cogitating about it, then we phoned and asked her and she said yes, she'd got the present. And phoned back a few minutes later and said no, she didn't think she had.
Eventually, to cut a long story short, we worked out that I never actually got the damn present - her birthday was the weekend after Eastercon and in all the rush of getting ready for the con, and being a bit ill afterwards, it simply slipped my mind.
So now I need to buy my niece a "sorry I missed your birthday" card and some vouchers. The silly thing is that if I hadn't asked we would have probably all assumed she had it, since I never usually forget birthdays. So it goes...