They explained that it's a serious condition where your blood glucose level is too high. There are two main types, Type 1 and Type 2. They're different conditions, but they’re both serious.
Having heard all about it, Ruby and a couple of her friends, Izzy and Emelia, decided to do something to raise money for the Juvenile Diabetes Research Foundation (JDRF).
They came up with the idea of holding a 'Pyjama day' and invited everyone in the school to come in in their pyjamas in return for a small donation.
Naturally, everyone rose to the challenge and on Thursday 31 March, a wonderful assortment of fluffy slippers, one-sies, dressing gowns and colorful pyjamas were being worn by girls across the school - some teachers even entered into the spirit too.
As Headteacher Mrs Brown explained, "It is so important that we encourage our young people to think of and support others, so I was delighted with this initiative.
"The girls' have not only raised awareness of a disease which affects almost 5 million people in the UK, they have also raised funds to support the important work that JDFR do."