why is my hair so hard to control??

I have thick hair that goes a little past my shoulders. It is impossible to make it perfectly straight! There`s this girl I know who has the same hair texture as me. Her hair is naturally curly. On the days when she wears it curly, the curls are shiny, bouncy, and frizz-free. On the days when she wears it straight, it`s shiny, smooth, sleek, and not so much as a wave popping out in the middle of her head. My hair is mix of straight and wavy. When I let it air-dry, it turns into a poufball of frizz and tangles that are supposed to be waves. When I blow-dry it, the top layers are straight, but the bottom layers (ESPECIALLY in the back of my head) are wavy and kinky and it drives me crazy! You would think that since my hair is half straight and wavy it would be easier to straighten then with curls. I don`t know how she does it. I need a GOOD straightening balm and anti-frizz cream. Does anyone have any suggestions? Thanks for hearing me out. :)