This has just been one of those days when life just happens, nothing major, just enough to interfere with things. I have tried three times to reply to you today, but as I said life happens, so I have not been able to do any more than just get started when I have to address other issues.
Lizzie sound to me as if she is hormonal among other things. IRN's are not the easiest birds to begin your introduction into the world of parrots simply due to the amount of time that is required to keep them from regressing to more wild behaviors, even though they have been bred and hatched in captivity. Because of the changes that should be made for your birds well being It would be helpful for us to know what part of the world that you live in.
It sounds like you work a great deal of the time and that makes it difficult for you to make some of the changes that are needed and because of that, I need to ask about your housemate and if this person is involved to any great degree with your bird as well as asking if they might be able to help you with the bird at least in helping the bird to have the interaction that it needs while you are at work. With the time of day that you are telling us that you are getting home, it is already dark, at least where I live, and that is why the question as to where you live. Perhaps you have the time to care for and interact with your bird more in the mornings and your housemate could take over in the evenings, so that the bird can not only get the exposure to the types of light that is needed to eliminate the hormonal behaviors that it and you are having to deal with as well as to allow the bird to get up and go to sleep more in tune with its normal waking and sleeping patterns. This along with some dietary changes will go a long way towards reducing Lizzies aggressive tendencies. Pajarita has stepped up and given you the basics of the changes that Lizzie needs and I am hoping to not only encourage you to make the changes but to help you find a workable way to bring them about. I am also hoping to help you to know more about why the birds requires these changes as well as how and why they affect the birds behaviors, so please feel free to ask any questions you need to.
So let's look at this hormonal thing a little closer so that you understand what is happening with it and why.
Birds are photoperiodic, which is to say that certain of their bodily functions are affected and controlled to a large degree by light as well as the type of light that they receive. They have an internal biological clock that is used among other things to measure the length of the day as well as the length of the light and dark periods of the day. The proper functioning of this biological clock is dependent upon the bird being exposed without interference of artificial lights, to both of the twilight periods that occur each day at dawn and again at dusk. These two periods of twilight set and reset the biological clock as well as acting like the start and stop switch on a stopwatch, so these two periods start and stop the period of measuring the daylight and dark periods each day. These measurements signal the birds endocrine system to start or to stop producing sexual hormones and so control the beginning and ending of the birds reproductive cycle. These same hormones also increase how aggressive the bird becomes. Diet is also a major factor in the reproductive cycle and in the amount of aggressive behavior that the bird exhibits because of the level of protein in the diet as the proteins are also used by the birds body to manufacture the hormones.
At the start of the breeding cycle the birds gonads are very small, which is a big help for the bird as they are all internal so space is at a premium. They are about the size of a pea in a bird the size of an African Grey, so they are even smaller in your bird, but during the breeding season they swell up and increase in size to over 100 times their dormant size. So although things get a bit tight inside the bird it is ok. The problem occurs when due to the amount of protein in the diet and or the light schedule of the bird is wrong and the endocrine system does not signal for the end of the breeding season so the birds body continues to produce hormones. When this happens the birds gonads continue to keep getting larger and larger and this increases their internal pressures far beyond their limits resulting in intense pain for the bird. In addition to this there is the additional pressures created by the gonads putting more and more pressure on all of the birds other internal organs, which increases the amount of pain as well as interfering with the proper functioning of these other organs. Eventually this pain will result in the bird plucking out its feathers and self mutilating itself creating big holes in its body as the bird tries desparetly to reduce and stop the pain. It also ends up creating a bird that can not tolerate even the lightest of touches due to the pain and so it bites to prevent being touched.
This is why the light schedule and one of the reasons for the bird being fed a good healthy low protein diet is so vital to the birds well being.
Here is a link
viewtopic.php?f=8&t=12521 that has a list beginning on the second page containing safe and toxic foods, woods, plants and other things for your bird. There are also several topics in the health, nutrition and diet section of the forum that can help you a lot in what and how to feed your bird a good healthy diet. We will be happy to assist you in this area as much as we can.
I am hoping that this will be helpful for you. I need to help a neighbor in just a couple of minutes so I need to close this for now, I will be looking forward to hearing more from you soon and will see what I can do to help you with the biting issues that you and Lizzie are going through when I next post here.