It was not very hard to do

After listening to Lily and Severus talk about being a witch or wizard for practically all her life, Petunia decides to forge a Hogwarts letter, hop on the train at King's Cross, go to Hogwarts and get a small job in the wizarding world. She's able to do it all successfully but comes to a dreadful realisation in the end one faithful day - it was not very hard to do.