Would you ever say elle était punie as opposed to elle a été punie?

Bonjour Jennifer !

Yes, if it was seen as a *background action* to a punctual one for example: "Ce jour-là, elle était punie dans sa chambre quand soudain elle entendit un bruit à la fenêtre." That day, she was grounded in her room when suddenly she heard a noise at the window.

Or, if you're talking about a *recurrent action* in the past: "Elle était toujours punie à la place de son frère." She was always grounded instead of her brother. Here are links to our lessons on when to use L'Imparfait: 

https://progress.lawlessfrench.com/revision/glossary/verb-tense-mood/the-french-continuous-past-and-past-habit-l-imparfait">https://progress.lawlessfrench.com/revision/glossary/verb-tense-mood/the-french-continuous-past-and-past-habit-l-imparfait">https://progress.lawlessfrench.com/revision/glossary/verb-tense-mood/the-french-continuous-past-and-past-habit-l-imparfait">https://progress.lawlessfrench.com/revision/glossary/verb-tense-mood/the-french-continuous-past-and-past-habit-l-imparfait
Using "si" + L'Imparfait in hypothetical sentences with Le Conditionnel Présent">
I hope that's helpful!

À bientôt !