To the OP, originally you mentioned drama, not musical theater . While actors certainly learn to move on stage, they don’t have to take the dance that musical theater actors do. Was the recent play at high school a musical? You also mentioned screenwriting.
She may be having temporary doubts about engineering before recommitting, or she may have a genuine desire to explore various areas of interest, including theater. Again, my suggestion would be to apply to a few schools, that cover each of her options. She can decide in late April. Encourage her to do things that help her clarify, whether that means more acting or classes/ lessons of some kind or volunteering.
I will also say again that a theater major is welcome in many areas of work and the skills learned are valuable in many fields. It is a bachelors degree like any other and gives access to grad school, or law/medicine/business/nursing schools after graduation. These days, many many students do grad or professional school and that is sometimes where the more specific career choice is made, if not on the job market.
I would try NOT to sway her at this point. About schools, majors, minors, anything. Except for financial concerns, let this be entirely her own decision but be there if she needs a sounding board. Reflect back in as neutral a way as you can manage 