If by 'redcap' you mean cabin crew they are operational crew and permitted I nthe cockpit, as is the engineer and dispatcher (ie critical to the operation) Discussion is pertaining to pax is it not? For interest, the OM-E also explicity states that pax are not permitted to visit the flight deck at 'any' time.
As for the girl in question, and selfies:
I don't think this is written down anywhere.
On the cabin crew end it is expressly prohibited to use personal mobile devices at any time while in uniform once past the e-gate, until reaching the hotel room. Exception is on the bus to the aircraft provided that the captain or purser do not need to address the crew. Ditto for the hotel bus.
This policy has always been in effect in my time in the company, however it was reiterated about 18 months ago and again when we got the new VP of cabin crew. It is also expressly stated on the portal. NO photos airside. NO photos in/of the cockpit. NO photos inflight for any reason except to document disruptive/security/medical incidents etc.
Sorry but them's the breaks.
So by her selfies alone, she has given them plenty to justify firing her.
(Of course it's a different ballgame when it comes to the 'Instagrammers'.)
PS - Girl in the Huffpost article recently left.