A female character is blessed/cursed with the uncontrollable ability to perceive time differently than those around her. At times, she slows down relative to the world around her. Everyone else seems to blur past her, and she seems frozen in time to others. And at yet other times, she speeds up. To others, she seemingly disappears as she moves too fast for them to see, and to her everyone freezes in place. Sometimes these last for seconds, sometimes centuries (if it’s her time frame sped up, centuries would mean she has an extended lifespan as well?).
The central theme of the story would be trying to control life, which is in essence out of our control. Also, the passing of time and the inevitability of death and losing those you love. The overall tone would be very bittersweet, but need to mix in some humor and romance. Once she realizes what her abilities are she shuns love, though some lovers insist upon trying and leave her sweet messages in parting when she freezes in place.
Not sure how to end it. I’m thinking perhaps she finally gains control of it, and decides to either rush through the remainder of her life, or wait it out to watch humanity’s story unfold.