Blood test would have been a culture,,usually they do three in a row and you have to wait for the bacteria to grow. Usually gram negative if assoicated with urinary tract infection.
More likely than not, the routine would be a CBC - which is a test which is very standard as it is a complete blood count. If her white cell count was not elevated they would not suspect an infection. Generally speaking, they don’t culture you if they don’t suspect an infection as the results take a couple days to see what grows. They let her go home. The article does not tell us all of the details of what happened. Other signs of infection are elevated temperature, tachycardia, low blood pressure (sepsis - but this is a lagging indictator)