"She is wearing her prettiest dress."
Translation:Hon har på sig sin vackraste klänning.
Could your please explain when do you add -e to the superlative adjective? I do not understand why one cannot say "vackrast klänning".
It's the definite suffix, you need it because sin and the other reflexive possessive pronouns trigger the definite.
However, 'dress' does not need to use a definite form 'klänningen' but just 'klänning'?
Yes, that's correct.
Generally speaking, if you have an adjective describing a definite noun, you need to put both of them plus a preceding article in the definite.
But if you have a possessive instead of an article, you put the adjective in the definite and the noun in the indefinite.
I admit it is confusing.
It seems I still have a long way to go in studying Swedish. :) Anyway, thank you so much for the help
You're doing great so far! You know the basic rule, you're able to apply it, and you notice that something's wrong when it suddenly stops working. That's a great start for the next step. :)
I wrote "Hon har sin vackrast klänning på sig" and it was accepted. 1) Is it an equally good way to say it, or only "acceptable?" 2) Is vackrast the correct form, or is vackraste required in my sentence also?
This is still a relevant question. I expected to see only "sin vackraste klänning" accepted, being the possessive + definite adjective quite a strong rule. Unfortunately, a lot of the more recent questions tend not to get an answer. If you come across the explanation on your own would you mind sharing it here?
EDIT JimNolt you can notice that the superlative adjective comes right after a possessive particle, and thus you need to put it in its determinate form which is "vackraste"
These superlative adjectives have been giving me fits. I keep the inflection tables open ( https://sv.wiktionary.org/wiki/vacker#Adjektiv ) when I do these lessons. Also, now that I realize that possessive pronouns trigger the definite (thanks to devalanteriel) maybe I will get more of these correct.