I think double majoring is way overated. I would take an average number of courses. As others have said the engineering major is pretty regimented. She will know soon enough what she can handle. After my first term freshman year I took one extra course beyond what my college required (which at the time was only four - no distinction if it was a lab course or not), and audited one course, but I usually took the extra course pass/fail. I actually got better grades taking more courses, but not everyone operates the same way.