What are the things we need to think about when we have to do a theatrical adaption of the poem "Daddy" by Sylvia Plath?
This is an interesting question! The first thing I would do is carefully read the poem and storyboard the plot line. This will give you an idea of where the action of the poem is and where you will need to augment it. It's not a long poem, so you either need to make up some events based on the obvious backstory or make it more of a skit than a play. You could easily make the themes of this poem into a play, but the actual plot will have to be made up.
Remember that not everything has to be literal. In addition to scenes of abuse, I also picture some very powerful metaphorical dream-like scenes, with the girl as a Jew and her father as a Nazi, since there is strong imagery of this in the poem.
“An engine, an engine
Chuffing me off like a Jew.
A Jew to Dachau, Auschwitz, Belsen”
I would also make use of the poem in the play as much as you can. For example, it might be the opening of the play, as a kind of prologue. It might also be spoken by the female main character at some point during the play, possibly broken up.
Since the poem addresses the abuse in broad strokes, making this poem into a play will require you to imagine what the speaker must have gone through. The play would show her interaction with her father and his abuse of her in various ways. It would indeed be a powerful play.