Well this is the big question, what was the accuracy of that final ping? I'm not sure how much cell orientated pinging goes on automatically and how many towers are involved in this, if it's one tower it's any part of a circles line she could be on, if it's two then it's two points she could be on and if it's three towers or more she could only be at one point, this is very accurate, draw three circles yourself all over lapping to see. Another way is via WiFi scanning, and maybe these days Bluetooth too. Or by location services/ timeline of the device which she had disabled previous night, this has the added accuracy of the phones gps receivers. In my opinion, if the ping involved three towers or possibly even two they would have been able to differentiate whether she was at the lake or on loxbeare drive at 8.34am. if no ping was done then it's by mast and this is wise area and therefore useless.
You also have to remember at furzton she is positioned between the fair and NM house so he/ or his friends could have been walking between the two or sat in vehicles first thing in the morning in the car park to keep warm out of site of the camera.
With the phone being broken, thrown or her simply not wanting to turn it on this would explain why she never called a taxi and opted for a bus.