Ela cuidava de você [quando você era bebê].
• She took care of you [when you were a baby].
• She used to take care of you [when you were a baby, but now she works for another family].
"Used to" implies a contrast with the past while the simple past simply describes a past situation.
For some reason I entered 'She used to care for you' which was accepted also! Maybe this can mean 'She used to take care of you' but I thought this might be a different usage - closer 'to care about somebody' for which my dictionary suggests 'preocupar-se com'.
Your dictionary is correct. It is interesting to see how, in English, "care for" can mean "take care of" or "care about;" it is one of those situations where the preposition can be ambiguous in the interpretation of its meaning.
Much like English, no? You can say "Take care of yourself.", and you can say simply "Take care", but I'm not a native Portuguese speaker, so I won't pretend to know the best translation for "Take care".