why is with THE mother wrong?
This sentence, with no further context, infers that it is actually "her mother" (com sua mãe / a mãe dela are also acceptable). But, as long as Duo loves literal meanings, THE should be accepted imo.
souldn't be this "...com a sua mãe"? -I just translated "...the mother" and was not accepted.
It's right too.
In Porguese, when we say things like persons of the family and body parts, usually we say it this way, and it's implied that it's "her mother", or "her hand".