"You're as bad as the old Irish woman who took the two pills to be sure, to be sure..." ?
Reduplication is an alleged trait of [Hiberno-English](to be sure, to be sure...) (Irish-English) strongly associated with stage-Irish and Hollywood films.
The first pill, she took to be sure, and the second, she also took to be sure, so together, she took two pills to be sure, to be sure...
There appears to be no idiom here. It must be from a book or other single source, wherein the meaning of this particular use may be found.
I can make a guess that it means one is as mistrustful as the old Irish woman who didn't trust that one pill would do the job, so she took two, but this is only a guess.