My oxygen deoendant baby has severe chronic lung disease will it take years for her to grow out of it. Shes in one litre of nasal oxygen?

Every baby differs. Every baby's clinical course is different. Keeping up with her medicines, if any, keeping her doctor's appointments and shots up to date, keeping your home and car smoke-free, and keeping her away from people who have infections are the best things to do to keep her lungs as healthy as possible. Her doctor will wean her oxygen down when it's safe.
It takes refocus. The length of time it takes to wean off oxygen varies greatly from child to child. Sounds like your baby has already announced to those who are observant that she is a fighter! rather than focus on the length of time it takes to wean off the supplemental oxygen, celebrate each day and the years and milestones that come with or without the need for oxygen.
A few more points. As she grows in height and weight, she will add new lung units which do not have chronic lung disease. These new units will help her wean off of oxygen. In addition, providing good nutrition and extra calories, will help her as well.