I've just read Anne McCaffrey's Sassinak. A book from her Planet Pirates Series.
Sassinak was thirteen when slavers kidnapped her and sold her twice for cheap labor. A Fleet officer befriended her and taught her what he knew. When she had the chance to be rescued, she in turn rescued the Fleet officer, Abe. Having no more family left (the pirate slavers killed them all), Sassinak was adopted by Abe and sent to Fleet school. The night of her graduation, Abe was killed.
It was on her first mission that she discovered Abe's killer and sent him to justice. She later finds out a hunch Abe told her long ago. There were insiders in the Fleet in league with the Planet Pirates. Sassinak vowed to find them and destroy them like they destroyed her world and her childhood.
At 40, she was now commander and captain of her own Fleet vessel, the Zaid-Dayan. With it, she was able to rescue one group of slaved colony. But it wasn't enough, not for Sassinak. She was led to Ireta, the mysterious Dinosaur Planet. There, she was reunited with Lunzie, her great-great grandmother who was younger than her. Together, they formed a team who vowed to eradicate the menace called Planet Pirates.
How was she able to be older than her great-great grandmother? Sassinak aged accordingly while Lunzie entered coldsleep one too many times. Coldsleep is a state you can put yourself in space so you won't age while you sleep for months and even years. Lunzie has two previous adventures giving her extra long life. Sassinak finds her at 36 while she at 46.
- On the way to Pern, the humans put themselves into a 15 year coldsleep to conserve resources and space during the trip to Pern.