Pronunciation of the pronoun: yours in unstressed position

Hello, the question: Is she a friend of yours? phonetically looks like
[?z?i(y)? 'fr?n?d?v y??rz?]

I think that the pronoun is unstressed as long I don't shift stress for emphasize. Right?

I checked the dictionary and the pronoun "your" can be pronounced as y??r, y?r, yo?r; unstressed y?r

However the pronoun "yours" only has the form "y??rz". There is no "y?rz" without that short '?' vowel. So, if I pronounce "y?rz" instead of "y??rz" is not correct. Am I right?