Application process for Taiwanese going to US?

A Taiwanese friend of mine will be going to the States to study and asked me what she has to do to visa wise before going. She’ll be going to California for a 3 month semester. Will she need a letter of acceptance from the university? It’s actually really pricy and she wants to get into another program, but I told her that might not be feasible without a letter of acceptance from a sponsor, that being the university. Anyways, I’m gonna get started on the search, but was wondering if anyone might have some helpful tips on the whole process that’s involved. Thanks.