Andromeda's Fall

Andromeda's Fall  - William C. Dietz Princess Ophelia makes herself Queen by killing the current ruler.
She then starts a purge of anyone who may still be loyal to her recently departed brother.

Catherine "Cat" Carletto is one of those on the hit-list. Being a wealthy party girl, she's forced on the run as one of the purges is taking place.
She finds herself at a recruiting station for the Legion - a combination of human and robotised troopers. An updated French Foreign Legion, they take people with no questions asked and allow them to choose any name they want.

The story is part of Dietz' [b:Legion of the Damned|722434|Legion of the Damned (Legion, #1)|William C. Dietz||708671] series, but you don't need to have read them to get into this book.

There's plenty of action both before and after Cat joins up, plus the new Queen sets up a special unit to track down anyone still on her list of undesirables.
The characters are well written, and there are plenty of tense moments from boot camp, being tracked and having to fight in an ongoing war.