There are a number of ex members who went very far up the bridge. Did several or even all OT levels, all kinds of stuff. So re your Mom, ya never know.
I suspect that everyone has their breaking point, last straw- the thing that really got through to him or to her.
For some, it's the information. CofS always had trouble retaining members because it treats people badly. But I think that when more and more people got onto the internett, that this really sped up the flow of members leaving CofS. And why? Because on critical fora and websites is information. Lots and lots and lots of information.
Has your mother read any of the writings of BlownForood (Marc Headley)? To me, that sort of thing is exactly what would cause me to leave if I were currently involved.
ESMB has tons of accounts written by exes of their experiences. These things dovetail, meaning that a lot of the same names, dates and places coincide in those accounts. Pretty damn coincidental for a bunch of tales told by lying bitter defrocked apostates, eh?