Mum disguised herself as her daughter

That disguise was wishful thinking on my part FiBlue. As the daughter was 19 I think it must have been a college exam rather than school.
But I can't fault your thinking. A double bare bottom spanking for mum should have been the order of the day. Then a spanking from the girls father when she arrived home after explaining why she couldn't sit to eat dinner. Phew! I think I need a lie down.

Always happy to help provide an excuse for more and harder spankings.
It appears to have been a baccalaureate exam that was given at a testing center, rather than at the school itself.

Then there's probably an office the two of them could wait in. usually some form of photo id is required for many exams nowadays. that could be the spur to detect the ruse. then off she goes with the examiner to the examiner's office. the daughter is summoned and then the canings or paddlings begin. I just might write it myself if no one else does. I already have one on the go so I would have to wait until the weekend at least before I could start.

Then, after all those spankings for pretending to be her daughter, a jolly good caning for failing the exam.

I always try and put a face to the ladies mentioned in situations like this.
Being from Dundee, I imagine the two ladies as Lorraine Kelly and her teenage daughter Rosie.
Lorraine Kelly fits the bill perfectly as a mature mum in need of a good spanking.

Yes, I do believe the mother plus her daughter should have been spanked. But with a cane. Yes, at least twelve of the best strokes on her naked rear end, after her bloomers were taken down.

There was a film about a mom who posed as her daughter to take the school entrance exam, and went to the store and dressed as a teenager, only to get caught in the dressing room. "May Contain Nuts". The daughter had nothing to do with it, beyond not being very studious; it was entirely the mother's scheme.

Of course in my version mom would be caught and as punishment she would get to go to the school for a full year, in uniform and under the constant shadow of the strict Headmaster's cane.