Spoiler; JKR cameo in CoS?

[TACtalk at adelanta.co.uk]

Not
really
much
spoiler
stuff
here,
but
just
in
case...
...
...
...
Just saw it again (6) and checked out the first witch in Knockturn Alley.
Heavily made up, of course,  but it could easily have been JKR. No mention
in the credits.

I too read a couple of times that CC said that JKR *never* visited the CoS set.

Didn't notice the woman on the station platform; if it was JKR, that could
get around that one...King's Cross is a location, not a set.

Regards,
Nicholas