Dear VG,
Your description indicates that your daughter's problem lies in her inability to tolerate frustration of her wishes. She experiences a rush of anger and quickly is overwhelmed with this emotion. She hasn't yet developed the capacity to manage the emotions associated with frustration. As you describe her, she sounds like she is otherwise developing in a normal way.
I endorse the suggestion of time out in the wake of any threat or action that is aggressive in nature. However, I would use an adult-size chair for the time out, not locking her in a room. Use a timer to track the time (probably around ten minutes), and start the timer only when your daughter is seated quietly in the chair.
It doesn't sound to me like your daughter displays an underlying mood disorder. But, if you seek professional evaluation, the clinician could discern if this represents (which I think it probably does) a normal-spectrum childhood behavioral problem, or is symptomatic of an emotional disorder (e.g., mood disorder, disruptive behavior disorder). One way or the other, the clinician could collaborate with you around behavior management.
Sometimes parents think that professionals should be consulted only as a last resort, only if serious pathology is evident. But, to be honest, most of the children and parents we see in the office are experiencing everyday types of problems, and they don't necessarily display serious pathology. Preventive guidance and straightforward help with parenting are probably some of the most useful services pediatric mental health clinicians provide.
Also add essential fatty acids to her diet. Read "The LCP Solution" by Jacqueline Stordy and Malcolm Nicholl. Controlled scientific studies have shown essential fatty acids to improve behavior because the cause of the behavior problem is likely to be an essential fatty acid deficiency.
My 6 yr old son was acting the same way as your daughter when he was 4 1/2. EXTREME tantrums that lasted 1 - 2 hours long 1 - 3 times per day with kicking, scratching, yelling, anger, out of control behavior at home and at school. We could take him no where because everything would set him off. We tried the two things I mentioned above and after two weeks we had a calm, compliant, obeying child. He verbalized his anger and frustration instead of acting it out. We are still on this diet and he still takes essential fatty acids. He takes a product called Efalex that contains the correct balance of Omega-3 and Omega-6 fatty acids plus DHA.
To improve your parenting skills try reading "The Defiant Child" by Dr. Douglas Riley. But at this point she cannot control her behavior and expecting punishments to help probably is unrealistic. If you need further information and support, the message boards at conductdisorders.com are excellent.