Search “change major engineering” at each school to find out how difficult it is to change into a different engineering major, in terms of GPA requirements and the like.
Also, compare curricula of the various engineering majors of interest at each school to see how common the frosh curricula are. The more common they are, the less chance of being “behind” if she changes major. However, this likely means fewer major-specific courses in frosh year, so there may be less opportunity to sample the various subjects to help her decide.
If the school offers a frosh seminar on what various kinds of engineers do, that can be helpful to help her decide.
Starting as an engineering major and then switching to math or physics should not generally be a problem, since the frosh engineering curricula includes the frosh math and physics courses. However, a few schools may have different versions of math or physics for engineering majors versus math or physics majors; if she attends such a school, she may have to choose the math or physics major versions to keep those major options open.