"She lives in a large house."

Translation: Ela mora em uma casa grande.

[Barbeito]

I~ve noticed that sometimes the adjective comes before the noun and sometimes after it. Does grande always follow the noun? "Ele mora numa grande casa" was rejected.

[erudis]

"Grande casa" is also correct. But keep in mind that some adjectives change meanings when placed before or after the noun, just like in French for example. In the case of "grande", it can mean "great" when it comes before the noun.

[Barbeito]

How interesting. I didn't know that, but then my French is no better than my PT. Thank you.

[gregdois]

I guess it would only be rejected because you used "Ele" instead of "Ela"

[Jason340994]

Why is it 'em uma' and not 'numa'?

[Captain_Zer0]

I lived in Brasil for two years and afterwards studied Brazilian Portuguese for a year at a university. 'Numa' was spoken more and taught as being more grammatically correct than 'em uma'.