Aww, that's awesome. I'm glad things are heading this way for you. Finding the right endo ( one that's supportive and available) seems to be like the hardest part for most of us, so it's great that it went that way for you. Now you just have to make sure you get that letter!
By the way, when your endo said she would like you to be cleared mentally first, did she give you the impression that she'd accept a letter from a pcp? Every endo is different with the letter "requirement", so I just wanted to give you the heads up just in case they will only accept one from a therapist. I know my endo required me to prove that I was in therapy and had their "approval" prior to starting treatment, but that's not the case with every endo.