I don't know what to do with her..

im really getting pissed with my girlfriends mindgames, granted thats what girls do but im starting to get smart enough and realizing them. for instance I know for a fact she was acting dumb yesterday to just get on my nerves. and when I confronted her about it and said stop acting dumb and straighten out she said I was acting mean and all she wanted to do was just make shure she got evrything right, and then when I asked her brother her own brother said that he deff saw that she was just playing with me, and its really starting to get anoying, but when shes not playing games shes really loving and I love her, so what do I do?