My best friend is a goof?

Well my best friend isnt crazy or retarded, she just sometimes gets out of control silly. Like after our soccer game she jept begging and begging my mom to take us for ice cream and it was funny at first but then it got annoying. And when we got to her house to drop her off, she got out and slammed the door which kinda ticked my mom off. (she was trying to be funny but...) and we were in her driveway for like 5 min trying to gently verbally pry her away from my car. Im kinda embarressed and my mom was kinda pissed. So how can i approach her about her "sillyness" cause shes super sensetive. Please please what should i do??? Also shes always saying shes fat and ugly when shes not.