When Barney dipped his face in the waterbowl like that, it seemed to indicate pain, as he stopped when on metacam for a few days. It coincided with him not wanting to eat his hay much. Never found out what it was though, had dentals done but there were only teeny spurs, and whilst it would stop whilst he was on the metacam for the dental, it would start again a couple of weeks after he was off it. Then it just stopped. And due to our finds about his gut recently, my vet thinks most of the times I had him in for dentals may have been a misdiagnosis of his gut issues, the pain in his gut causing him not to want to eat. We never found out what the dipping of his face in his bowl meant though really, apart from that it coincided with pain.
Sorry, I dont mean to say that she could have issues anywhere like Barney's, because he is just a big fluffy ball of problems, he is an older bun, and I think badly bred. But if you have a feeling that something is not right, and they arent eating properly and she is dipping her face in the water bowl like that - it could indicate a problem.