I seem to have zoned in on the subtext of whatever might have 'happened' that Polly is sorry for.
Polly gets big hair, big make up, Bon Jovi, crude re-imagined lyrics, working deliveries on Christmas Eve and credited with whatever misdemeanour that broke up their friendship while Lizzie, who is essentially employing Polly, is pictured with family, a natural palette and sensible haircut, a quaint cottage, a worthy banger, the Proclaimers and the grace to forgive her plundering ex bestie. It feels a bit caricatured, but perhaps it's not that deep.