It is written in ballad form.

Written in ballad form, the work is usually considered one of the last great traditional epic poems ever written in the English language.

The poem is written in ballad form.

He adopted the proletarian ballad form, and the author was credited as "C.3.3."

Musically, this begins with a very soft ballad form, gradually building into a "power ballad."

The song fades back into the ballad form from which it began.

The film is narrated in ballad form.

Written in ballad form, the poem tells of an artist ruined by love; having lost his beloved Madeline to another man, he has turned to drink.

The length of poems based upon specific song and ballad forms depended upon the specific tune or form selected as the model.

I think you're right about it being in ballad form - also with the poet herself belonging to the Irish Literary Revival.