The Twilight Zone - Spur Of The Moment

While out horseback riding one day, 18 year-old Anne Henderson comes across another rider, a middle-aged woman dressed in black, who chases after her. She's terrified and races home. It's the day of her engagement party. She's supposed to marry Robert Blake but childhood friend David Mitchell wants her to break it off and him instead. As for the woman in black, she is someone who knows Anne quite well.