I think your friend would have been returning to school from lunch as the crash was at 13.46.
I was at St Winifred's Primary School, Didsbury Rd, Stockport which is at the top of the escarpment to the north of the Mersey valley with a view across the Cheshire plain.
We were kicking a ball about when the Viscount flew down the approach. A few of us were interested in aircraft and invested 2/6d in J W R Taylor's ABC Civil Aircraft Markings every year. Movements at Manchester were comparatively sparse in 1957 so we stopped and looked.
As the Viscount flew past, we were whistled into line to go down a path to a football field at a lower level for the afternoon games session.
From our vantage point, aircraft disappeared from view at a point which I was later to learn was overhead Heald Green railway station.
As we started down the path to the field the aircraft disappeared. Seconds later a large column of smoke appeared close to the point we had last seen the aircraft. As nine and ten year olds we were curious about the smoke but did not link it to the aircraft until we were told, on the return to the classroom, that the aircraft had crashed.
Had the wind/atmospheric conditions been right we would have heard the impact as, in the right conditions, it was possible to hear aircraft engines at take off and full power whilst on the ground and, some years later the sound of Vanguards taxying was plainly audible.