"I haven't ever had a career, I used to say I don't know what I want to be when I grow up. So I used to enjoy helping out at school," she said.
At the time the school did not have a librarian, so Thomas asked if there was anything she could do to help.
The principal at the time then decided to employ Thomas. She worked as teacher aide in the morning and in the library in the afternoons, before she ended up in the office.
"I never imagined it would last this long though, who does?"
Thomas has seen many changes at the school in her 30 years, but the spirit has remained the same.
"It was quite a gentle school with the children, willing to embrace new ideas and it has just gone from strength to strength with that," she said.
"I just keep on meeting these fabulous people who are trying to do good things for children. So from the beginning that was how it was, and it has just stayed that way."
Thomas has worked at the school half her life. She said there are students at the school currently who are children of the students who were there when she first started.
She said they remember her and often say "you're still here Mrs Thomas".
"That's lovely. I have a good handle on lots of the families because of that connection," she said.
Thomas said she has loved working at Morningside School. She really enjoys the staff, fostering relationships, and - of course - the kids.
"We get some great kids that come in and say the most hilarious things that you take home in the heart - one little girl calls me Mrs Office."
Everyone has been telling Thomas how much they will miss her, and she's been getting little presents from students.
She said she will miss the camaraderie with the staff, and the smiling kids - but she's looking forward to spending more time with her grandson.
"I adore him to pieces and they just live down the road. My husband gets to see him during the day because he's semi-retired and they do things together with my daughter Harriet and I'm missing out."