Based on https://catalog.ucsc.edu/Current/General-Catalog/Academic-Units/Baskin-School-of-Engineering/Computer-Science-and-Engineering/Technology-and-Information-Management-BS , it looks like she would need the following lower division courses:
1 statistics course (STAT 5) (5 units)
2 math courses (MATH 21, 24 or AM 10, 20) (10 units)
2 economics courses (ECON 2, 10A) (10 units)
7 CSE courses (CSE 12, 12L, 13S, 16, 50, 58) (29 units)
and the following upper division courses:
7 CSE courses (CSE 150, 150L, 170, 171A, 171B, 175, 182) (29 units)
2 economics courses (ECON 100A or 100M, 113) (10 units)
2 upper division electives (10 units)
This totals to 103 units, which would take 7 quarters worth of courses if she takes normal ~15 unit quarters and does not need to fulfill any other (e.g. general education) requirements and schedules carefully with respect to prerequisite sequencing. Some overloading could get this down to 6 quarters. Of course, this could also depend on how frequently each course is offered in relation to prerequisite sequencing.
Do the three proposed courses cover ECON 10A (Economics of Accounting), CSE 50 (Business Information Systems), and ECON 2 (Introductory Macroeconomics: Aggregate Economic Activity)? If so, then they would cut the remaining major requirements to below 88 units, which could be covered in 6 quarters of ~15 unit course loads. Of course, if she is willing and able to do this overload this summer, she could overload in regular quarters as well (although beware of high workload CSE courses with programming projects). Any two would cut the remaining major requirements to 93 units, which could be done in 6 quarters with slight overloading.
The prerequisite sequences to note are:
CSE 12 & 12L → CSE 13S → CSE 182
CSE 12 & 12L, 16 → CSE 150 & 150L
CSE 50 → CSE 58 (winter only)
CSE 50 → CSE 175
CSE 171A (fall only) → CSE 171B (winter only)
ECON 2 → ECON 100A or 100M
ECON 2, STAT 5 → ECON 113
Note also:
CSE 58 is offered winter only.
CSE 175 and 182 are offered spring only.
Of the three proposed summer courses, those equivalent to ECON 2 and CSE 50 appear to be more important for prerequisite clearance than the one equivalent to ECON 10A.