Sorry about the long time replying, I was without internet for a while.
I am not sensitive about atheism in particular. I'm not an atheist. I'm not mainstream Christian, but I'm not an athiest.
I am sensitive about people equating different with evil. Without going into my personal life, I have spent a lot of effort and emotion trying to convince certain people in my life that I am not Hellbound for being different.
Maybe church would help the kid, I'm not arguing that point. I will say that the most hyppocritical, judgemental people I've ever met are in organized religion. There's nothing like having your Sunday School teacher who just taught you about love look down her nose at you for you clothing choices. At least I covered my cleavage and kept my bacon-fed knave tucked in my skirt, I can't say that much for most other girls in my Youth Group. Of course, your experiance may vary. Many people I know loved their Youth Groups/church time. I just didn't fit in and didn't care to pretend to.
(this isn't directed at Ulla, who I mostly agree with, but rather the others who see no problem)
When reading the OP, I got to that point about atheism and thought "so what?". There didn't seem to be any reason to mention it. Whether or not the DIL is atheist adds nothing to the account, and sticks out like a sore thumb. I doubt that the OP mentioned it as an example of the woman's bad parenting skills (at least, I hope not). But even unconciously, things like this happen all the time.
I will openly admit that I am an atheist, so I deal with this on a daily issue. People use the term in a negative way and never catch any flack for it, simply because atheists are such a minority. Imagine if I were to replace "DIL who is an atheist" with "DIL who is Jewish" or even "DIL who is black". See the problem?
To really see the effect that it has, imagine I were describing a secular charity (and made a point that it was secular), and then said "DIL who is a Christian". The obvious implication here is that there is a problem with being Christian, whether I would mean that or not.
I can understand the need to differentiate between people. For instance, if there were a group of people of whom one was black, I would say "the black person" simply because that sepparates them from the others. In this case it would be okay, but there was no reason to differentiate the DIL from the other people in the story.
I once again want to point out that I will give the OP the benefit of the doubt and assume she didn't mean it in such a way. I just ask that she think about the implications before writing it like that in the future.
Also, to Ulla, I doubt you are alone in the idea that more bad people come from religion than not, but I also doubt it is actually true. It makes sense that in a country with a 3-9% atheist/agnostic/non-believer population that only 3-9% of the bad/rude people you meet will be part of that same group. This means that 97% of the jerks you meet would be expected to be Christians. I doubt the number of jerks per capita is different between any religious groups.
This may be off topic, but it is an etiquette issue brought up by the OP.