I’ve plotted the list of roads the police put out for the dashcam appeal and, assuming the appeal relating to Cavendish Road was in terms of cars driving north, the streets plot a fairly logical route of:
1) Exit through rear of Leathwaite Road onto A205 South Circular adjacent to Clapham Common
2) Follow that down to the A205, bearing left (in SE’s shoes) to remain on the A205 at the junction where Cavendish Road joins it
3) Continue on A205 to where Clarence Ave joins it (note: Agnes Riley Gardens are the other side of the road here, so could be of interest)
4) Continue on A205 then cut corner near Tesco Express onto New Park Road
5) Continue on this to A23/Brixton Hill, which is the road with the Sainsbury’s Local that looks like the one from the CCTV
6) Continue up A23 then turn right into Brixton Water Lane. This is pretty much straddling Tulse Hill and Brixton, which may explain the mixed reports in residence
This in reverse may be the route SE took to her friend’s.
If she then retraced it after she left, it might suggest the Common was not actually entered on her return. But doesn’t rule out that she was taken in there from the A205, or any of the other green areas along that route - Agnes Riley Gardens, Rush Common, top of Brockwell Park. The latter two might suggest her phone could have died near Clarence Ave/Agnes Riley Gardens and she carried on towards home.
Speculating a bit here I know, but trying to fit in the places the police have listed, the time stamps, the Sainsbury’s CCTV and the developments of a search team at Brockwell Park. Leading me to think Clapham Common is not where she is.