this number calls me about 10 times per week

Its from Nigeria, she just talks rubbish, and tells me she is my friend, it must be a scam

If she is calling your cellphone you might be getting charged for the calls, which could be expensive if she's calling from outside your country. Contact your service provider, and have them block international calls, third-party providers and premium SMS to keep scammers off your phone and to dispute any charges from unwanted calls.