I’m guessing they already ran that unknown number. I’m guessing the FBI is involved because they suspect foul play. My guess would be she was kidnapped by a car jacker. It could be the person she talked to last. She might have been on her way to get the car back to her daughter but decided to make one last stop. I think it might have been planned because someone knew to turn off the phone as well as how to turn off the OnStar. The people she dropped food off to, did someone there call her back to return or make a last stop? Did she eat or drink something in that house? This is JMO but I think the FBI is probably researching all that right now.