Note: The following is my headcanon and my version of how I see my humanized versions of the MLP characters and does not affect the show itself. If you don’t like them then oh well.
 
Elizabeth “Betsy” Brauer comes from a German-Italian Family. Being the fifth child out of eleven children. Growing up with five sisters and four brothers. Because of this her life was anything but boring as there was something always going on in her house and her parents antique store. Betsy wanted to cheer people up and make them laugh. She would always throw people parties who are down in the dumps. However due to her weight and that fact she was rather annoying, Betsy would face constant bullying. This would actually make her feel sad and self conscious about herself but she was always confronted by her older sister, Maud, who was always there for her, and Betsy would keep throwing parties and making people laugh no matter how much people would make fun of her. Then came meeting Celestia and her new teammates. She was given the Element of Laughter which gives her stretching powers which allow her to stretch her limbs to incredible heights, transform into different objects, hardened her skin and body and to shapeshift into different body types, however despite this she still keeps her chubby appearance because she believes that is a unique quality of hers. Pinkie Pie is the comic relief of the group. Always making her friends laugh and cheering them up.(edited)