"My mother goes to her house."
Translation:Minha mãe vai para a casa dela.
It is wrong to say "Minha mãe vai para sua casa". The verb "ir" doesn't allow the preposition "para", the correct preposition is "a". So, the correct forms are: "Minha mãe vai a sua casa", if you suppress the article, and "Minha mãe vai à sua casa", in the case of using the article, causing what we brazilians know as "crase", that is nothing more than the junction of the preposition "a" with the article "a" or "as".
Can somebody please tell me when it's ok to leave out the definite article with the possessive adjective?? Is it only for family members??
If you use a possessive adjective (they're actually possessive pronouns in Portuguese) before the noun, you can drop the article (like in "minha mãe"), but if it comes after the noun you have to keep it (like in "a casa dela"). I'm not sure if that's a rule, but as a native speaker, it's what I've noticed.
But in spoken language people would probably say "minha mãe foi pra casa dela".