Give me ur opinion, is my mom unintelligent?

Ok so were driving in the car and she says some very dumb things like " you know why the car windows are dark" and I say " why" and she said " so you can't see inside and get shot". So weird but I kept my mouth shut, then she tells me that she doesnt want me taking protein supplements because it makes me angry, but what makes me angry is her weird and dumb comments, and how she says something one day and another thing the next day. The day following she says I'm lucky and she researched protein supplements and that they don't make you mad and that I can take it again, then the day after she yells at me and says that she never said that and that she would slap me if I ever say she said its ok to take the supplements. It pisses me off and stresses me out and I'm 15. I don't care what she says I'm still going to take them.