Andriana is a Greek national who will have been resident in the UK for 10 years on 1 April 2019.
Andriana will continue to have the right to exercise her free movement rights to live and work in the UK up to the point that the UK leaves the EU. As Andriana has been living continuously in the UK for over 5 years (without an absence of more than 2 years after that 5 years), she also immediately qualifies for settled status, subject to suitability checks.
This means she can apply for settled status under the new UK scheme once it is open. Once she has received her status and document she does not need to do anything further after the UK leaves the EU. Andriana will have successfully secured her immigration status in UK law.
It’s ok if Andriana hasn’t immediately applied for settled status. ….