Relatively unused by the Sicilian court until the 15th century when it was fed back from England like the Rima the Sicilian Septet had no pre-set meter, however English poets formalized the stanza to iambic pentameter. I’d say the choice lies with the poet. The rhyme scheme is as follows
The Kaiserin by Jez Farmer
Bavarian beauty, she reigned as queen,
Sisi her name, had no love for the court,
with grace and beauty she captured a scene,
a free spirit her courtiers couldn’t thwart,
as hearts were won, where ever she was seen,
the horse her choice of favoured riding sport,
Sisi became the German Kaiserin.
The youthful bride when history was made,
yet death still came and stole her beloved son,
In Mayerling, the place suicide played.
So dressed in black of mourning, still she shone
as fate lay wait with an assassin’s blade,
to pierce her heart under September’s sun
the socialite of beauty slipped to shade