This is a stretch, but it’s driving me mad so thought I’d ask!
It was an old children’s book, from the sixties. The main character was a girl, possibly called Jill (not the ponies Jill though!), or maybe Jenny? She had brown hair and was a farmer’s daughter. They were quite hard up, and her dad called her Pony as a term of affection. She made friends with another girl who was a vicar’s daughter, also quite hard up. Her name may have been Deborah? They bonded over the fact that neither of them had the correct coloured mac for school as their families couldn’t afford them. There was also a plot point where the main character was cycling recklessly and made their grumpy neighbour slam his car brakes on and break a load of eggs all over his car - Jenny/Jill had to go and clean it up and I think the grumpy neighbour turned out to be alright after all.
Any bells being rung for anyone?