edit There was an indication of Chiefly US informal, but if someone agree with @kcmurphy you/they could click ^ (up) under his/her comment, or say something so as to know more.
We use "seus, suas, seu e sua" for "your - singular". Almost nobody use this as "his" our "her", it's just on the highest formal Portuguese.
When we intend on saying something from "he" and "she" we say "dele(a)" or "deles(as)".
As meias dela são roxas - informal, common Suas meias são roxas - uncommon for third person, usual for second person.
Suas meias são roxas - common: Your socks are purple; As meias dele(a) são roxas - His/her socks are purple.