I think YABU simply because of her age. 18 is not an adult anymore. A lot of children don't reach adulthood until their late 20s.
I don't think you've handled the situation very well. You say you've not kicked her out, that she left of her own accord, but in her head I'm certain that she has left because she felt unwanted and unable to stay.
Many people don't seem to realise how difficult it is for young people to accept that they will need to work in a job they hate for the rest of their life, not to have a decent standard of living, but just to get by. The concept of working yourself into the ground just to survive isn't taught to them at school so it is a shock when they get to the age when they begin to realise it.
As they're growing up they're told that they can become whoever they want in life. They're told they will be able to find a career they will enjoy. They're told that if they work hard, they will succeed. This is all BOLLOCKS. The lucky few might find that, but for the majority life is just a long miserable slog.
You're daughter is at the point where she still believes the lies she has been told as she grew up and she can't understand why you're now telling her she has to get (in her eyes) a shit job for low pay.
In time she'll come to realise the truth. Like most people she just needs to hit rock bottom before she begins to stand on her own two feet.