Why did she look so different from DA:O? Was it because we were seeing her through the dwarf's story or what? Also, when is the DA2 story supposed to take place, is it happening at the same time as DAO?
Oh you mean that.
That could be one answer- she could be depicted differently through the dwarf's memory, yes.
Also it could just be that they wanted to make here look more cool and badass in the sequel.
Personally I imagined she has changed appearance since Origins because she's a shape shifter. Apparently she has also magically increased her age by hundreds of years and can make herself look much younger and more beautiful than she really is (but still reflecting some of her original apperance maybe).