How do you respond to someone calling you a liar and fat ***?

Someone did that my bf used to know but thinks she is a skank. Well thats my drama for this week. Tell me what you think I should do I have only seen this girl a couple of times. but everytime I do she plays nicy nice. She has never even been to our house or hung out with us. How does she know weather I am or am not lazy. Also I have a 32 in waist after 4 kids who is she to call me a fat ***?