Comics based on stories by Yasutaka Tsutsui (science fiction author who previously wrote The Girl Who Leapt Through Time and Paprika). Two volumes long.

[From Tokyopop]:

Nanase, a beautiful young telepath, returns to her hometown to settle down and lead a quiet life. However, her unique abilities make that impossible--even in the most remote location. Then she meets Norio, an abused little boy with extraordinary powers of his own. Nanase takes him under her wing, and from there they wander...two outsiders traveling from one strange encounter to another.

After 17 ordinary years on Earth, Makoto Konno's journey was about to be ended by a freak accident. Then, life gave her a reset button. With her new found time-leaping powers, she immediately sets out to wipe off all the little annoyances in her daily life, from failing grades to iffy relationships she can't handle. But as her time-leaps get more frequent, she is forced to realize that every change she makes has profound repercussions that she can't foresee...and should her powers fail her, the consequences could be disastrous...

This was set as a prelude to the 2006 animated film of the same title, which was in turn loosely based on the 1965 novel.

Taken from CMX website

Kazuko is a high school senior who has no idea what she wants to do in the future. Alone one day after school, she discovers a broken beaker in the science lab. She smells something sweet in the air, passes out, and finds herself transported back to her own past! Will Kazuko use her ability to travel through time wisely or selfishly?

Based on the 1965 novel.