I reject out of hand the idea that she should deconvert in the closet and systematically lie to everyone she knows.

I had to do this until I was able to sever myself from parental support at age 20. It certainly wasn't pleasant and sometimes I still have nightmares about being discovered breaking the Sabbath (though I've told my parents long since). But if you ask me whether I would have rather remained religious,

TEN THOUSAND TIMES NO!

Is it really essential that, as a community, we exclude or dismiss or reflexively criticize theists who are good at partitioning, who like and are good at rational reasoning in every other sphere - and who just have higher priorities than being right?

If Wednesday can partition, that puts an upper bound on her ability as a rationalist; it means she doesn't get on a deep level why the rules are what they are. She doesn't get, say, that the laws regarding evidence are not social customs that can be different from one place to another, but, rather, manifestations of the principle that you have to walk through a city in order to draw an accurate map of it. She can't understand the causality behind the rules, or she would simply know beyond all attempts at partitioning; she would no more be able to convince herself that faith works than convince herself that 2 + 2 = 3; it's a simple rule, and once you see it, it's obvious in one step.

In an absolute sense, God is no more plausible than Santa Claus or fairies. If you can believe in God, you can believe in anything. If Wednesday is amateur-level rational in other domains, then she may be able to contribute interesting comments to Less Wrong. But people, like chains, tend to break at their weakest link, not their strongest; and so being semi-rational in the domain of e.g. biochemistry may do her less good than you think.