Regaining confidence to ride after an accident
I would try the following:


Professional psychological (of course, if she agrees...);
Riding in non-traffic areas (a sinuous park or countryside would be great).


I have already perceived that most people learn a lot of bike-control while riding off-road-like situations, so that they become much more confident to ride in traffic, because the learned extra skills keep them comfortable to ride in everyday situations.

Well, just a thought, of course it depends on other factors. My wife, for one, is very scared of traffic, and sometimes trying too hard to give support ends up being an additional way to create stress.

Hope it helps, and good luck!