To ing or not to ing, that is the question:

To ing or not to ing, that is the question:

“Simon turned out the lamp and Eileen unbuttoned her dress, slipping it off over her shoulders, hanging it over the back of his desk chair.“

Excerpt from "Beautiful World, Where Are You?” By Sally Rooney

The two participle clauses don’t seem to depict one action interrupted by another nor two actions happening at the same time.

Rather, they seem to depict consecutive actions.

If so, the sentence could have been re-written (or edited) using verbs parallel to the second verb, ‘unbuttoned’, to depict one action following another:

Simon turned out the lamp and Eileen unbuttoned her dress, slipped it off over her shoulders and hung it over the back of his desk chair.