Even vacuums can’t distract mothers
Mothers can go Super Saiyan and possess unnatural powers when they sense their child is in danger. In this case, the OP’s grandmother felt a deep sense of urgency when her husband’s friend was pulling out of the driveway. Even though she was vacuuming at the time and might not have heard anything, her inner voice told her to go inspect.
Luckily, she listened, and she was able to stop the friend’s car from running into her daughter (the OP’s aunt). She stopped it right at the nick of time, too. If she decided against going outside, perhaps the aunt might have ended up in the ER that day.