In the Garden of Iden, by Kage Baker
I had a lot of fun with the Company series by Kage Baker a couple of years ago, and when somebody mentioned it recently I decided to do a re-read. This time I'm going to try to spot the giant, overarching plot elements when they appear early on, which of course I couldn't do last time--it's a perk of re-reading!
What happens if people in the future figure out time travel...but then it turns out you can't change history or visit a time after your own? And those same people figure out immortality....but it only works on small children with suitable characteristics? Well, they decide to go back in time and set up Doctor Zeus, Inc., which trains up immortal operatives who then collect samples and commission works which will just happen to pop up centuries in the future, bringing in wealth untold. Obviously.
And so Mendoza, who begins life as a dirt-poor Spanish peasant in the 1540s, becomes an immortal Company operative, a botanist trained to collect plants that will go extinct so they can be rediscovered in 700 years or so. Her favorite thing is breeding maize, but before she can be posted to the New World, Dr. Zeus sends her to England. She can pretend to be part of Philip II's entourage.
It's a fun, complex, and tragic series. By the end it's so bizarre and complicated that it defies summation. I'm looking forward to reading it again. It's currently out of physical print, but has just been released on Kindle.
I don't think there are any decent covers of this book. Each is worse than the last. At no time does Mendoza pilot a space pod.