Predicting that she will spill shit in my car meets the criteria for what a hypothesis is. We did these all the time in science class. A hypothesis is when you make an educated guess about what is going to happen. If I throw a bunch of metals into hydrochloric acid, my hypothesis (prediction that is not yet verified) is that aluminum will dissolve, iron will dissolve, but copper will not dissolve. It's just a prediction. Every definition of hypothesis puts emphasis on how it's not yet an observed fact.
While theory is as high as it goes, hypothesis can be promoted to fact. I started with a hypothesis, it was correct, it's now a fact. Facts are then used to support a theory which can never be completely proven true and can always be proven wrong. For the theory that my girlfriend is clumsy, a supporting fact is that she falls down. A supporting fact is that she wrecks her stuff as well as my own stuff. Under the assumption that she is clumsy, I put forth the hypothesis that she will spill things in my car. When it happens, the hypothesis is proven correct and it becomes another fact supporting the overall theory that is she is clumsy.