I haven't commented on this thread so far because I have been pondering it.
I would make it crystal clear that if she interferes with your job even if it is as little as hanging out in the parking lot making out and no one in the office could see her, that this arrangement is over. Why? This is your income. If you lose that income because you spend the end of the workday dealing with difficult child in difficult child-mode, then the entire family is in trouble. Protect your job even if it means that difficult child never sets foot on the property again. Unless you hate the job, in which case welcome her with open arms AFTER you have another job lined up.
Sometimes we get wrapped up in the difficult child problem that we forget to make sure that other parts of our lives are okay. it is important that you look at this from a big picture point of view. She needs t be on her best manners at all times around your and husband's coworkers', bosses, etc...
I can't imagine that she would be in a hurry to get home. If she knew I wouldn't be home for an hour or so, she'd stay out that whole time....if not longer.
This thought needs to be thought through, in my opinion. She is 17, clearly is interested in guys and sex, and has no place to have real privacy. EXCEPT when no one else is home, or her brother is home. She probably could bully and threaten to get your son to stay quiet. Think back to when you were a teen. If you were not dating, you knew kids who were. How many of them dn't want to be home unless a parent was there? How many of them skipped school or work or something so they could go have sex at home?
I could be off base, but if difficult child hasn't already figured out that it is relatively easy to bring a guy home for sex, then she will before too much time passes.