Haven't spoken to best friend in almost 6 months. How do I break the ice?

I admit I haven't been much of a friend. To give a backstory, I went into a deep depression. For a long while, I didn't want to get out of bed nor did I have any interest in doing things I used to love nor did I care to talk/hang with friends like I used to do. Showering and walking the dog felt like a lot of energy. I have had panic attacks & haven't felt like myself at all. I've been so scared because this is not me. I've completely isolated myself. Since Jan, I have been going to therapy after an intervention from family. It's been helping & my therapist suggested that I start trying to reach out to old friends. They have tried to reach out many times, but I have ignored them because it felt like a chore to even talk to anyone. Like the title says....I haven't spoken to my best friend in nearly 6 months. I have no idea how to text her to call me. What should I say? I miss her & my friends. I feel so terrible, I can't stop crying. I'm upset with myself for letting things get this bad.