To graduate in 4 years, she needs to take 15 credits a semester. As others have said, engineering tends to have set course sequences that are not very flexible.
A music major is likely to require significantly more practice and time than music as an extracurricular activity did in high school. One problem may be things like orchestra rehearsals conflicting with lab times. It is certainly possible to do a double major, but often students find that keeping music in their life as a minor or even “just” an activity creates less stress.
Sometimes, taking summer or winter semester classes can make the double major work out, but those have their own problems in terms of both stress and expense.