I did feel regretful, as you do when someone fairly harmless dies unnecessarily but I wouldn't put it as strong as sad - I didn't feel like I knew her so I didn't really react.

It scares me that people could be so utterly heartbroken over the death of someone they don't even know

Yeah, it did rather freak me out at the time. And I still get unnerved by the fact that there are people who go along every year and leave tributes and so on.