It's too late for your daughter, but the Essay it extremely important for borderline cases. Also taking the SAT multiple times till the math score is "high enough". About 9 years ago my wife and I went to an Alumni presentation where we did mock grading of applications. They provided a fairly high weight to the Essay, along with grades, SAT and extra-curricular. They said (and I believe them) that legacy didn't count. We had to rank 20 applications and only take the top 12. It was hard and would have been much harder with real people. They then showed us how our rankings compared to who they had actually accepted (names were made up and private info was taken out). We came pretty close except for the ones in the middle. A driving philosophical point is that GT wants to accept kids who will graduate; that's better for all involved. (School ranking goes up, kids get a degree, GT gets more money ..... everyone wins.) And graduation rates have been going up.
If your daughter has good grades and a low SAT, that is much better than average grades and a stellar SAT. Grades aren't all that is important though for classwork, it is also class standing and school standing.
Sorry I went on so long, this is as much for other parents on the board. GT hasn't had the Alumni presentation since we did it to the best of my knowledge.
Good luck!!