Diving Into The Wreck - Kristine Kathryn Rusch
1st book in the Diving Universe series.
And no, it's not it's not an undersea adventure.
Boss loves to dive historical ships, derelict spacecraft found adrift in the blackness between the stars. Sometimes she salvages for money, but mostly she's an active historian. She wants to know about the past - to experience it firsthand. Once she's dived the ship, she'll either leave it for others to find or file a claim so that she can bring tourists to dive it as well. It's a good life for a tough loner, with more interest in artifacts than people.
Then one day, Boss finds the claim of a lifetime: an enormous spacecraft, incredibly old, and apparently Earth-made. It's impossible for something so old, built in the days before Faster Than Light travel, to have journeyed this far from Earth. It shouldn't be here. It can't be here. And yet, it is. Boss's curiosity is up, and she's determined to investigate. She hires a group of divers to explore the wreck with her, the best team she can assemble.
But some secrets are best kept hidden, and the past won't give up its treasures without exacting a price in blood. What Boss finds could rewrite history, cost lives, and start an intergalactic war.