As @carachel2 stated, top 6% students are auto admitted but are not guaranteed their first choice major. If an applicant’s first choice major is not highly selective then the chances of getting accepted are high, on the other hand some majors are highly selective and only those “auto admit” kids who have strong holistic applications get admission to their first choice majors, but are then offered admission to their second choice major.
For comparison, accoding to someone who worked at UT admissions office, my son with a 1560 SAT (M=800, R=760), 99.83 wGPA and mostly 5s on 8 AP exams, only has a “small chance” of getting into UT Austin Computer Science department (no auto admission since he is outside of 6% at his high school). I think 80% of the seats are filled by the top 6% Texas students. The next 10% are filled by other Texas students outside of top 6% and then the remaining 10% are for OOS and international applicants.
OP’s daughter/son should count her/his blessings for being auto admitted to UT. There are other students (like my son) who would be thrilled to have the same opportunity.