Translation:Kateřina returned to her first husband.
BTW if you click on "Correct Solution" is unnatural or has an error" then we must assume that you meant the sentence written above as the official translation: Kateřina returned to her first husband.
We have no means to find out that you meant something else the system proposed to you.
Oh well, I didn't see that the translation above changed from the proposed translation while opening the discussion. I'll try to express my questions clearer. (BTW I'm not an english native speaker and don't know for sure if "came back" is a comparable translation, therefore I 'asked')
Generally, if you imagine a box, there are three ways you can approach the box:
- do +genitive: into the box, you'll end up inside it - which will then be v + locative
- na +accusative: onto the box, you'll end up on top of it - which will then be na +locative
- k +dative: towards the box, you'll end up right next to it - which will then be u +genitive
It's simple with a box. Then you have to learn which of the three pairs apply to specific objects/places/locations.
When you're at the doctor, for example, it's "u lékaře". When you're visiting František, saying you're at his place is "u Františka". Similarly, here we'd have "u manžela". And the direction to is: "k lékaři, k Františkovi, k manželovi", respectively. So that's for going to your husband's place or returning to him, and for more collocations.
"do manžela" would work with, for example, bumping into the husband - "Kateřina vrazila/strčila do manžela", or maybe if she gazed deeply into him like a psychic - "Zadívala se hluboko do manžela", or if she plunged a syringe into him - "Zapíchla injekci do manžela" etc.
"na manžela" would work with, for example, being angry at/with him - "Kateřina se zlobila na manžela", or if she sat right on (top of) him: "Sedla si na manžela", or also if she simply waited for him: "Čekala na manžela"
Prepositions are mismatched across languages, as you surely know judging by how many languages you've already looked into.