How do I get my mom to understand?

Whenever I ask my mom if my friends can come over to the house she always says " No! The house is too messy." If you go through the house you will see that there is not one thing of mine and my area of the house is completely clean. The things that make the house messy are her things all over the tables and everywhere else. My friends are also not allowed to come over because my sister's carpet has pet stains everywhere. Every time i tell my mom that i can't help the mess she yells at me for not cleaning my sister's mess up. How do I get her to understand that i can not help her or my sister's mess?