Her citizenship status should be invalid, I think she

didn't tell immigration officer that she has divorced
when she took interview.If she did so, her N-400 will be denied.
But even now, if the immigrtion officer find out the fact,she still may meet trouble.If this situation happen,your I-485 will be denied also, since her citizenship is considered no exist.
May be CIS officer won't put attention on the date of her dirvoce,if so,you will be fine.