cha ching said, " I have seen the propagandized lines of the WT take people's brains over right before my eyes."- I have seen that too and it can be quite scary when you first see it!
I wish you well with the letter. I hope she reads it but worry that her jw-ism will kick in and she won't get past many parts. Is there one thing you could start with? is she willing to have an actual discussion vs the usual jw cut and paste/parrot the wt style? I know how hellish those jw 'discussions' can be and perhaps letters are the way to go. If she can manage to stay on topic.