I go to a church which had a private school attached, one which achieves a barely satisfactory OFSTED report. The parents who choose this school (many of whom I am friends with) are fully aware of its shortcomings especially academically.
In one sense if you have personally known your dc's teacher for 10 years or more through church then the fact that their CRB hasn't come through isn't going to be such a concern: - the chances are you know plenty more stuff than would ever crop up on a CRB.
Now I would never and have never send my own children there (a point of controversy as we are on the leadership team of the church). However if I were to send my children to another private Christian school which has a better OFSTED ~(and there is one less than half a mile away) then I would be seen as deliberately snubbing my friends (including teachers at my church school). So if this particular school is attached to her mosque I would similarly assume that it would be a fairly major statement for her to choose a different school of a similar nature, especially if her faith, and her involvement in her mosque community, is an important part of her life.