I'm a fan of cathartic writing but I'm not sure she should send it.... Something similar happened to me with my sister-in-law, so this is more experience than anything else. I wrote down the good, the bad, and the ugly - EVERYTHING. I didn't send it but I felt so much better about everything after writing that I just put it aside for awhile. I thought about what I was proud of and what I felt badly about in the letter. When I finally saw her again, I was able to talk more cohesively, without the high emotion, and I got my points across much better and she was able to hear what I meant, not what what I felt. We still talk today.