@ai6yr yikes, that is so unfortunate. The law isn't unclear either: she was married in good faith, and they weren't separated or divorced. Unless her husband hadn't filled in a certain form, and even then, she could self petition. Again, this is an exploitation of the period of time thousands of people enter when their status is in transition. I hope she gets out soon.
https://www.uscis.gov/green-card/green-card-eligibility/green-card-for-widower-of-a-us-citizen