stuck in cistern/can not jump to last valve!

[Serena]

Forgive me if I am not understanding your problem correctly but - have you thrown a rock at the chain that holds the bridge up? Is that where you're having problems? I'm trying to understand exactly where the place you're describing is. I can't tell if you can't run+jump because you're in the wrong place (from what I'm thinking you are), or if you're trying to jump across without having lowered the bridge.
Can you describe where your problem is on this map?

-edit- worse come to worst... is it possible for you to get a friend or family member to work the controls and get Daniel past the part you're stuck at?