As much as you might want to save someone, you made the right choice, she was dead before she let go of the railing, she had already made her mind up. Who knows what troubles caused her to do such a thing, I feel for her family and friends as much I feel for her, she must have been very troubled.
The police have a difficult enough job dealing with this sort of thing on a daily basis, they have to be hard to it to deal with this sort of issue day in day out and even then most officers have regular counselling, just remember the police are human beings and anyone with any intelligence would know that you fall that far onto a hard surface most of your bones will be crushed or broken and your internal organs would just explode, she wouldn't have stood a chance CPR or not and the police knew that because they deal with it everyday.
Note: The ambulance were trying because it was their job, but it was a token gesture, not for the fact it would have saved her life. Also amatuer medics or professionals, you can do more harm than good, the police have to secure the area first having people rush in to help slipping on blood and hitting the girl would cause even more damage, the ambulance and paramedics are the one's to administer aid. You need a cool head in these situations not a rush and panic.
My Mates a copper and a good one at that and when you see a tough guy breakdown because he can't find a reason why someone wants to kills themselves and leave such carnage for others to deal with, then starts saying what if I drove faster, took more risks maybe I could have gotten there sooner and blames himself, sends a chill down you. So to all the police bashers out there before you criticise them walk a mile in their shoes, because I tell you you wouldn't last 10 yards.
Whatever the reason people commit suicide, its the aftermath they leave behind that gets me. So sad to see people in pain knowing they will never get answer trying to come to terms with it all.
May she now Rest in Peace.