Technically, the Garleans came to the waking sands to capture the Eikon Slayer, not Minfilia. Because we weren't there, she was taken instead only because she was leader (the "high priestess of the scions") and had the echo.

Also, no Sharlean scion (we know of) has the echo. Minfilia is Ala mhigan, as is that other guy still in the Sands.