Polygraph tests are not always accurate. It’s quite possible that she is guilty even though she passed. On the flipside someone could also be innocent and fail.
It’s true that they are USUALLY accurate, but NOT ALWAYS.... Mainly, if somebody is a psychopath/ sociopath then they are able to pass them because their heartbeat, body temp and blood pressure doesn’t get elevated from lying.
And rarely, someone can be super nervous and stressed but actually be innocent, but fail anyway.
If she’s coming home with bruises on her body consistently, then something is up. I recommend checking her phone records, that’s going to tell you a lot more than a polygraph will tell you.
Get the MOBISTEALTH app to monitor all the texts, calls, Internet websites, messaging, and apps used on her phone. And if she doesn’t let you, it’s because she’s cheating!