I was looking through bina and Chris's suggestions. University Maryland University College has online programs with three sessions so she might be able to do some online courses before starting at a bricks and mortar Uni in the Fall of 2017.
A couple of comments on this idea:
My experience via my eldest and online courses can be summed up as
caveat emptor. Be very careful. They tend to rely on multiple choice tests with questions about factoids. The questions can be badly written or deliberately written in a way that makes the question difficult to interpret. Instructor time can be minimal or non-existent. This problem is just as bad in the sciences and maths as in the humanities.
In addition, US colleges and universities have two basic routes for admission: as a first-year student ("freshman") or as a transfer student ("sophomore" or second year or higher). It's much easier (possibly
much, much easier depending on the institution) to gain admission as a first-year student.
This is important: if a student takes college-level courses AFTER getting a high school diploma or its equivalent, she will most likely have to apply as a
transfer student. I strongly suggest that you or your daughter check the policies at the colleges/unis you're checking before enrolling in an online course.
Other points:
US universities tend to distinguish between applicants aged 17+ and 16-. They see 17-year-olds as being basically adults like 18-year-olds. This is not the case for the 16-crowd, who are basically children in the eyes of the university. You have to fill out special forms giving your child permission to go to the university, and if you don't get all the forms filled out, the student's file won't be complete and the admissions people won't consider it. This requirement may not necessarily be spelled out up front. We have other members here who know more about this topic than I do.
You may also wish to read about problematic trends at US colleges and universities.
This article in the New York Times is an excellent description of the problem.
Be aware also that many professors use online homework systems (don't know how popular these are in Australia). They can be frustrating in the extreme, because you have to format your answer in a way that the software likes (and the software isn't always clear about its expectations). Online homework systems can also mean that a human will never look at the student's work and comment on it. I now tell my son to avoid these systems whenever possible, and he agrees completely. This means checking up each course before signing up for it.
How long will you be in the United States? If you'll be here for <5 years, will you have transfer options back into the Australian education system?
Finally, how much of this legwork is your daughter doing? My son is 14 and in 11th grade and is doing 90%+ of this work himself. IMO, this is really something the student should be doing. We talk to him, but he goes to the college fairs himself, and he explores colleges online himself.