As a person that works in the field (with trains) you would be surprised how many people kill themselves by train on our lines. I wouldn't be surprised to find out she was trying to kill her child. That was crappy video but it looked like she reacted late on purpose. I never really saw her head turn...but I hope to hell that is not the case.
I took a trip in Europe two years ago and our train was delayed because someone jumped in front of it, and I was shocked and a German friend said it happens all the time! Like almost more than a few times a week (but don't quote me on those stats). Crazy to choose to die that way if you ask me.