In one of the examples above:
Maintenant que ses parents n'étaient plus là, elle devait s'occuper de sa sœur.
However I'm confused because it states that Devoir with l'imparfait is "was supposed to [do]", however the translation is:
Now that her parents were gone, she had to take care of her sister.
Why is it not:
Now that her parents were gone, she was supposed to take care of her sister.