"She talks to her parents about everything."
Translation:Sie spricht mit ihren Eltern über alles.
Just guessing here but "mit" would be more appropriate when referring to conversing with someone since youre speaking "with/mit" and not AT them, as "zu/to" would seem to suggest. Could be used either way in English but I suppose it just isnt right in German, or maybe its a duolingo quirk.
Some German verbs take set prepositions.
Verb / Preposition / English
sprechen / mit / to speak sprechen / über / to speak about
The rule you quote only holds for "naked" accusative and dative objects (and only if both are not personal pronouns). But in this sentence we have neither an accusative nor a dative object. Both "mit ihren Eltern" and "über alles" are prepositional phrases, the respective cases dictated solely by the preposition ("mit" always takes dative, "über" is a two-way preposition). So there is no rule limiting their order.
And, btw., both are accepted here.
Perhaps you used ihrer (dative feminen)? Ihren is used though because Eltern is actually plural (parents). So you'd use the dative plural Ihren. Or to say it another way ihr is being used as an adjective here so it needs to be conjugated and with mit coming before it is conjugated in the dative case. I hope I've enlighten and not confused. I'm learning all these things too :-)
The following list of prepositions all take on the dative case. aus ausser (with scharfes S) bei mit nach seit von zu So if you used zu as a preposition, it would also follow with a dative case. However, I guess that using mit instead of zu sounds more formally correct and more intimate or friendlier when speaking with somebody. Zu is more used if you are responding to a question, such as, to where?, or when?, or how? I hope it helps. Perhaps a German academic might throw some light on the topic?
"sprechen", "reden" and the like are normally followed by "mit" in German, not "zu",
There is only one situation, where you can use "zu", and this is if someone ist addressing a huge crowd (may even be over the radio). Because then it is not a mutual conversation, but a one way communication. That's what the "zu" indicates.
So in normal conversational situations always use "mit".
Because that's the correct form of the pssessive "ihr" in dative plural.