Need Advice - how to decline invite during COVID19

My best friend is having a birthday BBQ today. I don’t want to attend because I’m am practicing social distancing. I do have type 1 diabetes one of the 3 CDC highlights as higher risk category not to mention I’m pregnant as well. I’m completely scared to leave my house. My friend does not take social distancing seriously. How do I decline the invitation? Her sister is coming in from out of state to celebrate with her.