I don't think you were being too harsh.
I mean, depending on what career she wants to pursue, she doesn't have to go to college. But, if that were the case, I'm sure she'd make that clear. I'm assuming you mean college, not high-school.
As for the job, perhaps she can't get one, so she doesn't want to try anymore? I've applied and sent inquires to at least 8 workplaces since I've been 18 (almost 8 months) and I've yet to get any calls back, not even to inform me that I didn't get the job (which, after several weeks, is apparent). But then again, I'm sure you'd know if she were trying to get a job... or not, depending on your relationship with her (I pretty much tell my mom everything).
There is nothing wrong with hanging out with friends, to a point. I guess, it depends on how they influence her and vice versa; is she doing the "bad things" they do? And if spending time with them distracts her from doing what she's supposed to do; didn't pick up little sister from violin practice because she was with her friends.
I think that, maybe, instead of sending her away, you should have talked with her about your/her expectations. Even if she doesn't go to school or get a job, she still can lead a responsible life. If she is being irresponsible because, perhaps, if you feel this way, she's only getting on your nerves.
Regardless of your plan of actions, she's an adult now (although, not necessarily a grown-up), so getting her back into your house isn't going to be easy. Once we (older teens - young adults) have a little bit of freedom, we run with it, and many run fast.
It all comes down to communication.