Kissing passionately, kiss her on the ear, and then move down to the neck. Caress her breasts, etc. Pull her very close to you and hold her tightly. If she's responding to your moves, then she's horny. Kiss your way down and kiss her body. Start fingering her while you're kissing her. If you're both comfortable, you can do oral on her. If none of these work, then she's either too uptight, not ready, or is just not attracted to you.