A normal academic year would be 3 quarters (a full 4 quarters would include the summer quarter as well as fall, winter, and spring quarters). If she intends to use summer quarter for school, then she needs to take into account which courses required for the major are not offered in the summer quarter when planning her schedule.
If she decides to back off to two summer courses, CSE 50 and ECON 2 are more important than ECON 10A for prerequisite purposes. Note that CSE 50 is a prerequisite to CSE 58 which is offered winter only, so it is desirable to complete CSE 50 in summer or fall in order to take CSE 58 in the winter.
Assuming that she takes CSE 50 and ECON 2 in the summer, then her fall schedule should probably look like this:
- CSE 12 & 12L (important prerequisite)
- STAT 5 or CSE 16 (preferred for prerequisite reasons), or any other course required for the major
- residential college required course
If she does not take CSE 50 in the summer, it is best for her to take it in the fall (along with CSE 12 & 12L and the residential college required course).