Betsy - Does her triggered ability go on the stack even if the controller didn't pay the cost?

[split geyser]

Just curious if there's a window to respond regardless of whether the controller pays resources or not.

[lilac minnow]

There is. Betsy's trigger condition is 'did an attack I control wager?'
The trigger that goes on the stack is 'you may pay 2{r}. If you do...'