For some girls it can take upwards of 1-2 years before they become really regular. Normal cycle lengths can vary from 3 weeks to 2 months. I would not be concerned about her continued irregularity at this point.
I suspect that over time her periods will become more regular.
Advice and opinions given are based on the information provided and must not be considered an official medical recommendation. The limitations of the internet prevent an appropriate evaluation. Always consult your doctor if there is concern.