My reading is different - she knew he was incarcerated and came to visit and ended up marrying and staying - OP, what visa did you enter on? Or was it VWP?
OP's spouse still has another 6 years before release.
OP, the quotes USCIS guidance clearly says MAY - not a must, may. That could trip you up as they can choose not to go without your spouse's presence. There's no obligation on USCIS officer to follow the may guidance.