The daughter of Born To Sea created a big impression when winning at the Curragh on her racecourse bow in August, and was pitched into Group One company next time out in the Moyglare Stud Stakes.
She was not disgraced in fourth, running on markedly different ground to that she encountered on her debut and finishing behind three Aidan O'Brien-trained runners.
Lynam said: "Muirin will go for the Fillies' Mile on Friday. I'd say the ground was too soft for all the fillies last time (in the Moyglare), but it was a good renewal of the race.
"She has been in good form since and will appreciate some better ground."
Fourteen fillies are in contention for the race, including the first three in the Moyglare - Happily, Magical and September. Ellthea (Karl Burke) and Magic Lily (Charlie Appleby) have been supplemented.