I would get a second opinion because I think the advise from your lawyer isn't right, see below:
"An application for an EU3 Permanent Residence Card which is made on the basis of retained rights will not be accepted unless the non-EEA national applicant has already been approved for the retention of their Residence Card on an individual basis.
An Application for the Retention of a Residence Card can be made on Form EU5. Retention of a Residence Card is required where the EU citizen of whom the non-EEA national is a family member has died or departed from the State, or in the event of the divorce or annulment of marriage between the non-EEA national and the EU citizen."
I am not a lawyer or immigration counselor, all views expressed are my own, my comments do not constitute legal advice.