"I must warn you about her."
Translation:Jag måste varna dig för henne.
What about "Jag måste varna dig om henne"? I'm trying to figure out why för is accepted and not om.
I think that's mostly just because different languages make different choices. för is often used in contexts like this, we've got förvarna which is like forewarn in English, there's this sense of 'before' in it, a bit like 'I'm warning you before you meet her, so you can be prepared'.
The same preposition is used in combinations like rädd för 'afraid of' where the thing is sort of 'causing' an emotion.
varnade om is not a natural way to put it in Swedish, it sounds like a bad translation from English to me.
Thanks, that does help. It's easy (for me at least) to memorize words but much harder learning how to make the sentences sound less... google translated.
What if one was to say, "I must warn you (as a favor) for her", would the preposition be different?