If convicted, she could be forced to register as a sex offender for 10 years.
"If we lose this, she's on the sex offender registry with child rapists and things of that nature," her lawyer, Randy Richards, told the Salt Lake Tribune.
"The magnitude of the penalty on this is enormous."
The stepmother is now fighting the case.
"It was in the privacy of my own home. My husband was right next to me in the same exact manner that I was, and he's not being prosecuted," she said.
Prosecutors in West Valley City argued she was "under the influence of alcohol" when she removed her shirt and made a comment that she would put it back on only if her husband exposed himself, local media reports.