You can almost completely undo the power of disappointing HS grades by getting a 3.7+ in college. Knock it out of the park in college, and transfer targets will care a lot less about what happened in HS, especially if you’re applying with two or more semesters of grades on the books. I got into Harvard, Stanford, and Penn as a transfer with a 3.9 college GPA and straight Fs in high school. I’ve seen others do roughly the same thing many times in the last 15 years.
I disagree with menloparkmom. The whole point of using HS transcripts in the admissions process is to predict college performance. If you have an applicant with 2 or more semesters of ACTUAL college performance, why would you care what the predictors have to say?