I don't see how you could have any level of trust whatsoever at this point. Your wife is a serial cheater who was busted and did not confess. You know of two affairs, which means , in many cases, there were more that you do not know of.
What, exactly, is the peoblem with a polygraph? She will not object if she is remorseful and truthful. What is the big deal about verifying the statements of a known liar?