She wears a purple cardigan with a pinkish shirt under. She has blonde hair and wears glasses. Mum also wears blue jeans and pink shoes.
Throughout the show, Mum is shown to be quite stressed and irritable most of the time. Her favourite food is Tickly Treats and in Horrid Henry and the Tickly Treats Thief, she loses her temper when she mistakenly thinks Henry has eaten them.
Mum, along with Dad, is completely and utterly living in denial over Peter and Henry. Mum always believes Henry to be the one who does the bad things, and never Peter. This is proven in Perfect Peter's Horrid Day when Mum is telling Henry off for putting slugs in the chocolate box, and Peter says out loud "But Mum! It was me!". Mum then continues telling Henry off, and then hugs Peter and praises him afterwards.
She treats Henry unfairly for most of the time, sending Henry to his room and calling Peter seemingly unfair names like "sweetie bunny" and "darling", but never calls Henry any of that. She also acts slightly meaner to Henry than Dad, and even in one episode she got Dad in trouble. Another sign of unfair behaviour is on Horrid Henry Happy Birthday Peter, which is where she says it was lovely that Henry could have the chance to disappear, much to Margaret's disgust.