McCaffrey, Anne. Dragonriders of Pern.

Dragonriders of Pern

Young Fiona, rider of the gold queen Talenth, has returned from the past, where she and a group of dragons and riders fled so that the wounded could heal from their previous battles with Thread and the younger dragons could safely grow to fighting age. Gone only three days, yet aged more than three years, Fiona is no longer a child but a woman prepared to fight against the Thread that threatens to destroy her world. Fiona's life takes a pivotal turn when a shocking tragedy thrusts her into a position of authority. Now she finds herself leading weyrfolk who have a hard time trusting a senior Weyrwoman who is both young and an outsider