If this is her clothes, why not suas roupas?
Yes, it seems that both "sua roupa" and "suas roupas" are both correct. See here: https://www.duolingo.com/comment/1025077
Another example of the flexibilty in translating singular/plural nouns:
Eu compre muita roupa nova. (I bought a lot of new clotheS.)
Can someone explain to me why the "me" comes before "mostrou"?
there's an in-depth explanation on pronoun placement here: https://www.duolingo.com/skill/pt/Clitic-Pronouns