Don't know if you still need this, but at least for others in the future: 1) Hon = She
2) har på sig = wears/is wearing (think literally "has on oneself"). You can write the clothing being worn either between "har" and "på" or after the whole thing. It makes no difference.
3) sin fina klänning = her nice dress. "Sin" is the reflexive "her," referring to the she from the start of the sentence. "Hennes" would mean "her" referring to some other woman. We use the definite form "fina" (indefinite for an en-word like klänning would be "fin") in possesive cases like this where the adjective is before the noun. "Her dress is nice" would use the indefinite: "Hennes klänning är fin." If we said "the nice dress" it would also be the definite adjective and then dress would need to be definite too: "den fina klänningen."
You could use that and other constructions, but it would change the meaning - e.g. hon har en fin klänning på sig = she's wearing a nice dress.
The "use the definite instead of a possessive" thing doesn't really work as soon as you have an adjective involved, because when you do, you also need either an article or a possessive pronoun. Hence, you could say en fin klänning or den fina klänningen, but neither would mean "her".
Of course they can, but Swedish frequently uses a definite in lieu of a possessive if can be assumed that the thing belongs to themselves. It's a perfectly legitimate question.
I don't understand why you'd add the latter part. It was just a question of how to use the language, not a complaint about the course.
I was basically responding to the sentence, "Isn't it clear that dress belongs to her if she is wearing it?" The answer to this question is no, so indicating that the dress belongs to her isn't necessarily unreasonable or redundant.
Given the way the question was asked, I interpreted that to mean Norravargen also wouldn't say this sentence this way in English (the question I just quoted applies to both English and Swedish). I see this issue brought up from time to time, where people question when they'd ever need to say a certain phrase learned here. Maybe I misinterpreted.
I get that, but Swedish actually isn't as clear-cut - I'm actually leaning towards that the definite can be defaulted to instead of the possessive unless there's a reason to believe otherwise here.
That's fair enough, and I know exactly what I mean, I just really don't interpret the post the same way. :)
I'm guessing you looked up "nice" in an older dictionary? Nizza is the older Swedish name for the French city of Nice. :)
fin can also be "beautiful", and we accept nice / pretty / beautiful / fine here. Generally, though, "beautiful" corresponds best to vacker and "pretty" best to söt.