It’s too far fetched. If she said she saw 200, well, maybe but 4000? Nope, I don’t buy it. That would be just in the area she was in too, not the entire island and the Bolivar to High Island area. I doubt that the Bolivar to High Island area has much more than that in population even in the summer months. Even when 3000+ people died in the WTC, did any one person see that many?
If one accepts the posit that 85% of the people who didn’t evacuate had cell phones, telecoms could count the number of accounts with no recent activity or GPS signal - underwater or otherwise not working.