You can apply for citizenship 90 days before the 5 year mark, not 6 months.
But since she is still in legal status and the F2A category is current across the board and will remain current until September 30, she can file for AOS anytime between now and the end of September. Then when you become a citizen you can get the petition upgraded to reflect your citizenship. Make sure USCIS receives everything before October 1.
EB3 ROW I-485 Approved: July 2007
USC: July 2013
I am a layman, not a lawyer. What I write here is not official or professional legal advice. In addition, my answers on this forum are specific to the scenarios discussed in each thread and should not be generalized to other situations.