It’s normal for snakes to do thatI’ve seen my BP drink droplets from misting off of his hide, or even drops of water on the sides of his water bowl while a full bowl of fresh water is just sitting there.
I think it’s an instinctive behaviour snakes developed in the wild because they most likely will not easily come by standing pools of water (especially true for snakes in deserts or hot climates). Standing pools of water can also be more risky to drink from because other larger animals and potential predators are drinking there too. Snakes have to be opportunistic and likely rely on drinking dew, fresh rainwater, and any other moisture they come by, even if it’s just a few drops.
Also, your BP probably does drink from her water bowl, just very secretively. It’s a vulnerable position for them to be in and I have only seen my BP drinking from his bowl a handful of times in 2 years. If I catch him drinking and I move or approach him, he will instantly shoot back into his hide.