Referencing books in your personal statement is never a good idea. They don't want to see that you have read books etc. They want to know why you want to do the degree, why you're inspired to do it and tbh reading a psych book is hardly the reason why you chose the degree. All I can suggest is that you tell the absolute truth. In mine I admitted I've had a tough life, I have friends with mental health issues, I have mental health issues and my sister died ect. You need to sell yourself to them, referencing shouldn't be in your personal statement. Honestly, go on to the UCAS website, they have guides to help you, if you need any help I'm always happy to help. 😊