Vicious Circle by Elle E. Ire

Assassin meets innocent. 

Kicked out of the Assassins Guild for breach of contract, hunted by its members for killing the Guild Leader, and half hooked on illegal narcotics, Cor Sandros could use a break. Down to her last few credits, Cor is offered a freelance job to eliminate a perverse political powerhouse. Always a sucker for helping the helpless, she accepts.

The plan doesn’t include Cor falling in love with her employer, sweet and attractive Kila, but as the pair struggles to reach the target’s home world, pursued by assassins from the Guild, Cor finds the inexplicable attraction growing stronger. There’s a job to do, and intimate involvement is an unwelcome distraction. Then again, so is sexual frustration.