I'm highly doubting this is Samantha Mathis - after all, Samantha was a friend of the family and let's face it - fans can spell Joaquin's name correctly, a friend sure as heck would be able to.
I was hoping to find a board to post on about my memories as a fan living over the other side of the world - but this place seems more content with abusing each other and posing to be people you are not. Neither honour River's memory or his family who were left without their loved one. It's just down right disrespectful. So I think I'll find somewhere else to write - I just couldn't leave without pointing out the most obvious reason this person is not Samantha Mathis.