need help to write a recommendation letter 1

I am applying for nursing and I need a recommendation letter from hospital that I was volunteering for. However I was not working inside the medical facility but I was working at the hospital store as a volunteer and I have been doing that for a while. I asked her to write me a recommendation letter but she told me to write one myself and she will see what she can do. I have no idea how to write a recommendation letter so I need help. So I want this to be written as if she wrote it for me.