Definitely include letters of support even ones from other family members welcoming her into the family. We did that and had first time success. I included a letter from my three sons. Also you say print outs of yahoo conversations. I would avoid giving them anything like that - it's not necessary. Just print outs of chat logs will suffice, not the actual conversations. Too much information will just be irritating.
Incidentally we put ours in a proper lever arch file and each document was in a plastic sleeve. The first thing the checking staff did was remove all of the sleeves and bin the file! They just put a big paper clip on the whole lot.

Best of Luck

Dave and Lolita