I noticed at the first few chapters of the book, it was shown that Bella was saved by Edward in a car accident at their school. After that, she was sent to the hospital even though she was not that hurt. At the same emergency room, there lies Tyler Crowley, the one that almost crushed her with his van, bleeding vigorously.

On the next chapters when they had blood testing in their Biology class, Bella becomes faint at the sight and smell of blood.

Why didn't she faint at the hospital when Tyler was being aid by the nurses to mend his bleeding wounds? Why did she faint at the Biology class even though it was just a droplet?