Does evidence have to be medical?

After sending off my ESA50 I have now had an appointment for a f2f. I've been in SG for 5 years. I have multiple problems and have only ever had the initial medical in 2006. Last reassessment was in 2013 and I appealed for the SG. It took 2 years but I was successful.

After studying as much as possible over the weekend, I've come to the conclusion that I'm being sent for f2f as I didn't have any recent evidence to send. Although I've had a lot of therapy over the years, my last lot finished 3 years ago. I rarely see the doctor and have meds delivered. Do you think a support letter from my best friend would be acceptable. She knows me better than anyone and has seen how my health problems affect me. She is going with me to the f2f so could I take the letter to that? She's very honest and doesn't hold back but would they just assume everyone is lying?

I don't know what else to do about supplying evidence. GP service is massive and there is always a different doctor. No personal knowledge and too many patients to deal with.
I sent my old supporting evidence from my therapist this time, but I assume that would be too old.

Of course, I'm terrified and feel constantly sick and tearful. They've given me less than 2 weeks notice for the f2f so there's not a lot I can do. Would be very grateful for any experiences or advice.

Thank you for your answer Gordon. And the help you provide to us all in general.

One thing I don't understand is the difference between LCWRA and Support Group. I've searched everywhere and can't work it out. It's probably really simple and my mind is playing tricks as usual.