Owned By the Irish Mobster by Oona Ryda

Saoirse Keane has spent her life surviving—fourteen foster homes, years on the street, and a world that taught her no one is coming to save her.
Then one night she sees something she shouldn’t.
A mob hit.
The man who pulled the trigger is Declan O’Rourke—Chicago’s most feared enforcer.
Cold. Controlled. A man who eliminates problems without hesitation.
And now she’s one of those problems.
Declan should end the witness and be done with it.
Instead, he make an offer she can’t refuse.
Marry him. Or die.