I would recommend your daughter plot out on paper a 4 year program putting in all the requirements for both majors plus all other requirements such as general ed classes, course prerequisites etc as a basic guideline. This would help her see how the dual degree would fit together and can it be done on time just taking 12/13 credits to start. My major wasn’t a stem major but required two internships. By taking 18 credits most semesters I was able to reduce my credits the semesters I did my internships to 15 and 12. My last semester senior year I was doing a 20 hour a week internship plus commute time,weekly internship meeting (no credit but still took up time), senior seminar which was basically a capstone class for my major and required me to teach a 2.5 hour class with a partner, write a 15 page paper etc. and take another class to maintain my full time status. I also remained active in some activities and focused on job hunting etc. I think it would have been difficult to enjoy my last semester needing to take more classes due to starting light but found it easy to start out with 18 credits. I also worked 5-10 hours a week all 8 semesters at a work study job though I changed jobs after my freshman year to one that offered more flexible schedule.