Having worked in a professional office as both a letter-writer and letter-reader dealing with similar issues, I have to say that Scully's letter (with the proposed revision above) is the way to go. As general advice for everyone, never send a letter like this without dates and other concrete details. That's how you make your case best.
It will be interesting to see if your cousin brings up the religious issue when speaking with her supervisor. If she does, I have to think she'll be in some serious hot water.
I admit that I have some of the same concerns others raised about the issue of going to her home (above and beyond what's required of her), but that could actually backfire against her in the sense that, as mean as she was to you, she was actually giving preferential treatment to you as a customer by taking them to her home and meeting with you after hours. The professional thing she should have done would have been to find a way to get them to you during business hours, even if it involved sticking them in the mail for you. I imagine that will be something her manager notices immediately as problematic. You never, ever have clients go to someone's personal home for a business matter, even if it's in the complex. Too many liabilities there.
In any case, best wishes with this!