"It is her brother's thing."
Translation:Это вещь её брата.
No, it's not. The normal word order is:
- Declinable modifiers are put before the noun.
- Indeclinable modifiers are put after noun.
(Её and его are expections to this rule: they are indeclinable, but they come before the main word!)
'Declinable' means the word changes its form to show the gender (краси́вый па́рень 'handsome guy', краси́вая де́вушка 'beautiful girl', краси́вое ме́сто 'beautiful place'), number (краси́вый па́рень 'handsome guy', краси́вые па́рни 'handsome guys') and case (краси́вая де́вушка 'beautiful girl', краси́вой де́вушке 'to the beautiful girl'). Usually only adjectives and some pronouns are declinable.
Indeclinable are those modifiers that don't show case, number or gender. Бра́та belong to this category: де́вушка бра́та 'brother's girlfriend', па́рень бра́та 'brother's boyfriend', ме́сто бра́та 'brother's place' — бра́та stays the same, unlike «краси́вый». So, we put бра́та after the noun.
See my comment here for another example: https://www.duolingo.com/comment/11877095
Sometimes we can change the word order, especially in poetry, but it doesn't sound well in normal speech.
Sorry, I should have been been clearer. It's declinable on its own, but as a modifier it doesn't agree with the main word in case. This is the main difference: вещь брата, вещи брата, вещью брата (брата is always in the same case), but братова вещь, братовой вещи, братовой вещью (братов matches the main word in case, number and gender).
I've just copied it from the browser's URL bar. I use Firefox and the Desktop web-application, I don't know if it's possible to get these links in the mobile application.
Hm... «Эта вещь — её брата» is theoretically possible, it's grammatically correct, but it's not how I'd say this phrase, it feels less natural. Not sure why.