People aren't things to be managed -they have thoughts and feelings too.
I think it may be your inflexibility which may be contributing to your daughter's anxiety.
What does 'grow up' really mean anyway? Maybe we're considered 'grown up' once we meet someone else's very unrealistic expectations of us. Expectations that push us further away from ourselves.
Talk to your daughter. Ask her what it is she really wants. Voice your opinion and perhaps qualify it but allow her voice to be heard too. Don't feel you need to quash all her dreams because they don't meet your expectations. Killing a persons spirit is one of the worst things you can do.
Perhaps you could also look at what her behavior means to you. To me it almost sounds as though you have placed conditions on your love for your daughter.
I sense that you are extremely proud of her. I think exerting some independence is a good thing. I think it does indicate that she is growing up.
Just be extremely careful how you manage the situation.
It is difficult for me to say what the best way to proceed would be, in part because I don't know your daughter the way you do, obviously. And it is not clear from what you wrote why your daughter is panicking (I don't know if you have any ideas). It might be helpful to help her figure exactly what she is panicking about -- what is it about entering the workforce? Is she afraid to fail? Is she afraid to leave home on some level (most young adults are loathe to admit this, by the way)? As far as how much you should "put up with this stuff," that is a judgment call on your part, depending on your own resources, and your sense of your daughter's ability to deal with uncertainty and anxiety. Has she shown the ability to be a "self-starter" in the past? Has she looked to you to solve her problems for her? How is her frustration tolerance? These are some of the questions to ask yourself that may help guide your decision about whether or not to give her a safety net.
Two other thoughts: 1) As you are likely well aware, right now is the worst job market for people graduating college in recent memory. So even if she wanted to get out into the job market, there aren't a lot of options. So going back to school may not be the most unreasonable idea (even if it is motivated by fear).
2) I am aware that different parents have different levels of tolerance of their young adult children continuing to depend on them (financially, for a place to live, spending money, etc.). Some parents have the attitude that once their child has graduated, they're on their own completely. Some parents are much more flexible. You are faced with having to figure out where you stand on this, and that will depend on your own values as well as your knowledge of your daughter, as I described above.