This is possible, but
@hawkeyefan will need to weigh in on what swimming away through the swamp water means -- if the hag was described as submerged initially, then I don't think your analysis is preferable to one where the GM was just presenting the nos in order of their grasp of the fiction. To that, I can see the GM thinking the hag's last move would get them far away, but this was countered by the player. Then the inability to detect the underwater hag seems reasonable, but again the player has a counter. Finally, the ability to shoot into water is used, but this seems reasonable. Had the GM initially considered and realized the first two objections were countered by player abilities (not that easy in 5e with so many possible and the already large GM overhead), then they could have deployed this final step first and the issue would not have felt the same. As I look, I'm don't see the GM creating new fiction to thwart the player -- that seems to have been done well to start. It's the walkthrough and repeated nos that feel off here.