'Is it fancy dress?' I reply, alarmed. The only disguise I possess is a French maid's outfit, required for a long-ago murder evening at theological college. I don't think it will be suitable for me to make a public appearance with the Vicar in a frilly garter.
She is bemused. It is not fancy dress, but every female guest has been haunting TK Maxx to assemble a killer look for the occasion. Now I am bemused. My nights out number three or so a year. When it's curry evening with the Ladies from the Choir I don my chunky-knit dress in case of draughts. When, more rarely, it's a Do I rely on my funeral suit. It's the only garment I possess not made of pilled wool. It has never crossed my mind to buy an outfit.
Now it's half an hour before the party starts and the 11-year-old has confiscated all my black viscose. I reach resignedly for the chunky-knit. The 11-year-old repeats her daily lament: 'Why do you always have to embarrass me with your uncoolness?'
Fortuitously I remember a piece I read in The Sun while hanging around the barber's. Celebrities, it seems, have been eyeing my woolly distinctiveness with admiration. Exhausted by the effort of looking exactly the same in their designer bling, they crave the individuality of a BHS cardie. All these years I have, unbeknownst to my daughter, been cultivating 'post authenticity' according to the New York trend agency K-Hole which has identified the new craze for looking ordinary. Normcore they call it.
Jack Wills must have clocked my polyknits on my reluctant visits with my tweenager, for its creative director says he's working on introducing The Special Ordinary and The Perfect Boring to its clothes rails. My matronly look, carefully nurtured over decades of M&Co sales, proclaims, he says, my uniqueness, soul and intelligence. Even Vogue has acknowledged that my corduroy smocks, the labels bleached blank by 12 years of hot cycles, express 'ingrained authority and inner confidence'.
I explain all this to my daughter who is looking mortifyingly 'yesterday' in Juicy Couture sequins. I fancy she looks sceptical, but I'm certain that under cover of darkness she'll be creeping into my closet to try out my tweeds. I know too that the trendy young mums will soon be jettisoning their Louboutins and their Pauls Boutique and begging loan of my bobbled cardies.
It's a new sensation for me to be a fashion guru, but I feel it's only fair to share my expertise in readiness for their transformation. The important thing to remember is that the Normcore look should combine utilitarianism with thrift and a total indifference to style. Here, therefore, are the essential steps to Perfect Boring Ordinariness (while sparing your wallet the strain of Jack Wills):
Junk those salon stylists and curling tongs. Invite a trusted friend round for a Gordons every six months and hand her a pair of scissors, then all you need to do is filch a rubber band from the postman.
Ensure you choose cardigans with snug enough sleeves to lodge a store of tissues (BHS slouchers tend to lack pockets). The cardigans should include the colours of at least two different body fluids to ensure longevity amid family life.
Try to choose corduroy bootlegs with elasticated waists for flexibility should you suddenly need to entertain guests on the trampoline.
Footglove flatties from M&S suit every circumstance from putting the bins out to a night on the tiles.
All your efforts at boringness will be undermined by an unsuitable mobile phone, so keep that iPhone 5 for pillow talk - this is the must-have handset on the school-gate catwalk.
If you have any tips for those disillusioned fashionistas do share them here.