To answer your question, which school she should pick. UPenn is known for its business school, wharton MBA program is probably one of the best if not the best MBA program worldwide. Nonetheless, b/c she is a Chemical Engineering major, she should probably narrow her choices between Michigan and Princeton.
In terms of location, Princeton is probably a better choice, since it is New Jersey, which is not far from New York and Washington DC. In terms of academic, probably Michigan is better.
She can ask recommendations from others, but ultimately, it is going to be her choice, regardless which school she end up picking. It is her life, she should ask herself which school do i like the most, do i prefer to live in a big city and experience the culture or do i want to live in a small town atmosphere and possibly produce some outstanding research work.
Hope what I wrote helps and God bless,
Shuo