This OP did not lose eligibility when her husband, an EB immigrant, naturalized. She became an IR eligible for concurrent filing as she did have a lawful admission in the first place and that is all an IR needs to be eligible to file for adjustment. OP began as a spouse and continues to be a spouse of the same person through whom she is applying for adjustment as his spouse.
If you are going to quote from the AFM, quote from the relevant part:
(G) Dependent Adjustment Applications.
In order for a dependent applicant for adjustment (e.g., an alien whose original adjustment application was as the spouse of a sibling of a U.S. citizen)
to convert his or her adjustment application, the principal adjustment applicant (in this case the sibling of the U.S. citizen)
must maintain continuing eligibility up until the time of the conversion request and the relationship between the principal and dependent adjustment applicants must continue to exist. If there is a break either in the principal’s eligibility (e.g., due to the death* of the U.S. citizen petitioner) or in the relationship between the principal and dependent (e.g., they get divorced), the dependent’s adjustment application cannot be converted.
Note
However, (assuming that all other considerations are met) the dependent is not required to convert to another dependent category. For example, an alien who meets all the other considerations could convert from applying for adjustment as the spouse of the sibling of the U.S. citizen to applying for adjustment as principal applicant under a first employment based category.
*DEATH of petitioner is no longer an absolute denial in light of the new INA section 204(l) as described in:
http://www.uscis.gov/USCIS/Laws/Memoranda/2011/January/Death-of-Qualifying-Relative.pdf
ALSO: "One cannot interfile a denied I-485." {Incorrect, it's already IN the A-file.}
"Also, a break in underlying eligibility for AOS before the interfiling request also would disqualify the interfiling." {There is no such thing as an "interfiling request", she will request "conversion" from one category to another.}
"The existing I-485 became ineligible for approval when the primary naturalized," {Technically, this is correct, but there are too many IF's requireed for that to happen since the underlying application is in regressed visa category, it's sitting on a shelf untouched, and they don't know he naturalized until they file the I-130 and request conversion at which point USCIS is alerted to the situation and won't deny the I-485 because that is reversible as plain error and it would be malicious.}
".....based on their interpretation of eligibility for derivative benefits. So USCIS may deny the I-485 before the I-130 is filed, or respond to the interfiling request by denying the I-485." {Not likely for a regressed visa category that is sitting on a shelf awaiting progression of the Visa Bulletin.}
