By making a composite chart between you and the girl, using both natals, you could get an idea of likelihood of marriage.
Your natal would show timing for marriage possibilities, even the likely type of woman you would be ideally married to, but would not answer a SPECIFIC question about a SPECIFIC woman.
Horary would answer as to a specific woman for marriage; however, that answer would largely be time-limited, and to obtain a clear answer you should ask "will x and I be married within y period of time": now this y period of time, could be projected out perhaps to a couple of years, but beyond that, well, life situations are so changeable that we are better off (accuracy-wise) to limit our time-frame to a shorter period...