So this is because плаття is a trick word right? Looks like feminine, but is actual neuter?
"Сукня" is feminine hence "ваша". "Плаття" is indeed neuter. Why does it seem like trick word to you?
Because it ends in "ya", which implies feminine. It's one of the 'exceptions' we need to learn (as a neuter word that is disguised as feminine). Thanks for the clarification!