Non EEA partner PR refused on dual nationality

Hello everyone
Highlights are in processing times thread got refusal in 5 weeks of postal application.
Reason being partner has dual nationality. Similar to McCarthy case my 5 year one was granted on feb 2014 after extensive interview. British passport was expired and was never renewed but had it before in past.
Solicitor advised of two options
1) Appeal the case on basis of good Friday agreement as partner can chose to be Irish or british But not sure how its gonna look if she already had British passport. (Costing around 2000 and gonna take 6/8 months)

2) apply FLRM which i know nothing about apart from i might lose my right to work and that her British passport has been expired 3/4 years so might have to renew it.

Please advice as i have very limited number of legal advisors here in NI.
which way to go from here i am totally lost
Many thanks

When did you apply for that Residence Card which was issued in 2014 February, you may have fall within the transitional provision, and if that is the case, then they cannot now do this as it will be unlawful.

Thank you obie for replying.
These are not accurate dates but as closed to as i can remember.
I initially applied for the COA (certificate of approval) sometime late 2010. Never heard of them and it was abolished in 2011.
Applied for RC in july 2013 was interviewed in January 14
Was issued on 18th February 2014.

Just adding further info, the similar case recently won Appeal but HO appeal against it its emma desouza vs uk
The partner in that case was issued with LOTR for 5 years.
Only difference with that is my partner had her british passport but was expired some 5 years ago and was never renewed.
I also added my daughter's Irish passport just in case it would help a little but they just disregarded it.

The Shirley McCarthy judgment was made by the ECJ on almost precisely the same point (of a Northern Irish lady wanting to engage EU free movement law in spite of having never exercised treaty rights) in 2010.

Thank you simon for the reply, Yes i understand that but my initial application was closed to transition period and i was awarded RC based on same circumstances plus recently developed story https://www.google.com/amp/s/amp.thegua ... a-de-souza
I am just wondering if i have grounds of appeal
Thanks