Another newbie, here, I’m afraid, so apologies for any mistakes...
I live on Leathwaite, very near to where SE started her journey from and one thing that has always struck me from the beginning was, why she left the friends house by the rear gate? The garden she’d have to walk through would be dark, and you come out onto a small piece of scrub land (completely unkempt and overgrown), before you get to the South Circular Road to follow around to Clapham Common. It would add no time at all to leave the friend’s house by the front door and follow the well lit road around. I know SE was seen well after this point of her trip, but maybe it just shows that she wasn’t adverse to a little detour, even across an unlit, uneven area?
The other thing is her phone being turned off. I know someone previously asked if turning her phone onto “flight mode” stops all ping activity (I definitely do that myself, if my battery is dying, and especially if I wait to listen to music). I have to admit another bad habit I have, especially after a cheeky vino or two, is if I have an argument on my phone, I’ll hang up and turn my phone off, so they can’t call me back.