[Sundae]

British:
Any Ealing Comedy (tell her to Google it)
The pronunciation is always RP and easy to understand.
But they're all black & white and therefore might be "too old".
The original The Lady Killers or Kind Hearts and Coronets are excellent though.

The original St Trinians films might speak to a young audience - black & white though they are. She'll have to view them first though! Attitudes have changed!

Otherwise maybe Four Weddings...? Again, I'm not up on the age of the kids. It was a 15 over here (15 being the lowest age to watch the film at) but I remember there being bad language.

Shakespeare in Love? They'd probably hate it.

Brazil?
Maybe too avant garde. And shows nothing of culture really, just subversive attitude.

Can't she show them a Dr Who episode instead?
The Christmas specials run to an hour.... And they're nearly films (in that they're mostly stand alone and therefore accessible). And there are Dr Who books and figures to turn them onto after all....

Or an episode of Morse or Midsomer Murders (both modern day murder mysteries that are shown at teatime, so aren't violent). Both of those show beautiful countryside - ahem, from around my part of the world - AND rural values. Even if they are stereotyped. But isn't anything relating to culture?

If she can deal with Edwardian England there is also The Railway Children (film from a book). I'd be suspect of that in a culture lesson though. You'd have to teach that it was from a bygone era of steam trains and nostalgia.

It's tricky, because we make mostly period films, horror (and I mean REAL horror) or comedies with significant adult content.
I'll keep thinking though.

Did my best for you on the British front babba.
Good luck to her anyway.

Sundae aka Ultimate Brit.