"Sarah's comment is rather telling in spite of the fact it is ostensibly ___"
The key seems to be the word "ostensibly".
On the surface: apparently, evidently, externally, ostensively, outwardly, seemingly, superficially. Idioms: on the face of it, to all appearances.
Are you trying to say that the comment that Sarah made is telling in spite of her apparent, contrived or otherwise, lack of guile.
In other words, is she making the comment to let the facts be exposed (ie dropping someone in it) while retaining the air of unintention?