In these verses the order of events is somewhat confusing, it is written this way to emphasize how the water brings the curse. It seems that the woman drinks the water, the priest burns the offering, and then the woman drinks the water again. She only drinks the water once, as is make clear in the UDB translation.
It may be helpful to reorder the information in these verses by placing verse 24, that give information about the woman drinking the water, after verse 26. The UDB translates these verses in a similar way.
# a representative offering
The handful of the grain offering represents the whole grain offering. This means the whole offering belongs to Yahweh.