I think the original may be incorrect here - the translation of the above should be "Είσαι η πιο όμοÏφη κοπÎλα που Îχω δει στη ζωή μου" - this one means "You are the very beautiful girl that I've seen in my life"
Hello smy Kafetzou is right: What it says is "You are the very beautiful girl that I've seen in my life" which is as irrational in Greek as it is in English. It is in all probability meant to say "You are the most beautiful girl I've seen etc" but I'm afraid it doesn't