I am going to give my girlfriend an ultimatum.
Why are you giving your girlfriend an ultimatum?
She criticizes me for being unable to figure out my life.
While I understand that it might be frustrating to have your girlfriend criticism you, an ultimatum in not the best way to handle it. It is important to have open communication and talk about your problems instead of resorting to unhealthy things such as ultimatums.
But she is totally wrong, and she needs to be shown that
Your girlfriend thinks that she is doing what is best for you.  She doesn't realize that it is so frustrating to you.  If you just talk to her about how you feel, she will understand, and you won't need ultimatums.