Trying to understand Lightning Network better, and risks involved.

If I want to pay Bob, and I have opened a channel with Alice, and she has an open channel with Bob, it seems straightforward: I pay to Alice, she pays to Bob.

What if she refuses though after I pay to her? Is there a way to make it atomic and trustless? If so, can anyone point to the description of low-level protocol implementation of this?

The only thing I can think of is streaming satoshi-by-satoshi (you risk only the first satoshi), but that would be extremely verbose, noisy and slow. And if there are more intermediaries in the chain than just Alice, it's even worse.