Based on the sample schedule at https://che.engineering.ucdavis.edu/undergraduate/degree-requirements , it looks like the curriculum is fairly traditionally organized, starting with mostly natural sciences and math, followed by engineering sciences, and then getting to engineering design at the end (using the prerequisite knowledge from the natural sciences, math, and engineering sciences). In other words, the “good stuff” (the engineering design courses) is mainly in senior year. If she switches out of the major now, she will miss the “good stuff” (the “hands-on” design aspect of engineering).
(Note that this type of traditional engineering curriculum organization may be “efficient” in handling prerequisites, but it may cause students to lose interest because they are in engineering to do engineering design. So some engineering programs throw in some design course work earlier to keep students interested, even though the scope of such earlier design courses is more limited.)
Specifically, the four year course plan lists design courses in senior year (among other courses):
Fall: ECH 158A
Winter: ECH 158B, ECH 155
Spring: ECH 158C
https://che.engineering.ucdavis.edu/undergraduate/expanded-course-descriptions has more detailed descriptions of the courses.
As a practical matter, if she is completing junior year, changing to a different major is likely to delay graduation. Also, while 180 units are needed to graduate, if a new major would require going past 225 units and 12 quarters, that may not be allowed.