If she hired a private polygrapher, then she has him.  His paycheck comes from her.  So, there is at least the appearance that he might be working the results in her favor.  It does happen, and it can.

Does your wife know CM's (countermeasures)?  It's easier to beat the test by using proper CM's on control questions than it is to flat lie on "Did you have sex with (whomever)?"  However, it's not impossible to do the latter, especially with some practice, ability to control the emotions and certain parts of the autonomic nervous system, and knowledge of arts that allow for such control, like yoga.

For a deeper look into the poly, CM's, and how these things run, read George Maschke's "The Lie Behind The Lie Detector," available free on the front page of this site.  I have read it 4x, and it is very enlightening.

If your wife is in some form of rehab, as I gathered, and is kissing guys in there, you've got marital issues which you must deal with that make a poly look like nothing.  It's not your fault, though, man... infidelity on her part is -her- mortal sin, if she's engaging in it.  Sounds like she admitted kissing one or more 3-10 times by the tenor of your post.  Call me old school, but I would be very distressed if my wife kissed another man with amorous affection even once.

If she tells you she passed, so?  Note above: CM's, control of emotion, perhaps a sympathetic polygrapher, perhaps a new or incompetent one...

Add all these up, toss in whatever her emotional state was, is, might be, how, when, where the test was administered, and so forth.  It's a dynamic, changing encounter and test from minute 1.  She says she passed?  I'm underwhelmed, sorry.  Even if confirmed by the polygrapher, see last paragraph.  This sort of thing is why both sides in a court case get to examine a witness; otherwise, you're only getting one side of the story.

The poly is rife with ways to manipulate it, my man.  Count it as nothing.  I've never been married, but I can say this: if you think she's been cheating on you, trust your gut.  Confront her, talk to her, ask what's up, and do some good old-fashioned digging for info if you must.  Don't let your marriage's future rest on some squiggly lines.  You have the right to complete honesty from your wife, as she does from you.

I pray she has not cuckolded you, and that things get better for you and your marriage.  Good luck, amigo...

You guys need a marriage counselor far more than you need a polygrapher.