Power was appointed to the NSC in 2009. She had all the security clearance she needed to unmask at any time.
It seems we are pretty lax in removing security clearance.
People long gone still have it.
http://www.businessinsider.com/susan-rice-keep-security-clearance-2017-8
An important issue to be dealt with in and of itself, to be sure.
The point here is S/P's full-time job was being UN Amb.....not intelligence-gathering.