The actress, who plays Billy Mitchell's granddaughter Lola Pearce, revealed that she had never had an audition before and did not expect to get the part.
Harold told the Daily Star Sunday: "I've always wanted to be an actress. I didn't do very well at school because I became ill in my final year. I worked for a local catering company but I couldn't stop thinking about being an actress. Every night I would search the internet for acting schools.
"I've been very lucky to have been given such a great character and I still can't quite believe everything that's happened to me. It's been a whirlwind."
Harold added: "[Lola's] had a tough upbringing and needs some stability, which Billy provides. I've already had letters from kids who have grown up in care homes saying how much they love Lola."
Harold, who starred in Jamie Oliver's Channel 4 reality show Jamie's Dream School, recently revealed that she is a big fan of former EastEnders cast member Lacey Turner (Stacey Slater).