The local nobility just so happens to be incompetent enough that they can't tell the difference between a band of Baphomet worshippers undercover in the local bureucracy, and a huge sized snake monster with a mirror for a mouth.
It's quite absurd, when you put it that way. Perhaps there were Baphomet worshippers and they summoned the snake. Perhaps the local nobility wanted to get rid of her specifically, and so they arranged for a monster. It's medium treason, so they could even get away with it.
In any case, it's too late for the speculation to lead to any useful actions. Her Hellknight escorts are dead, and the snake is closing in. She uses her Ray of Sickness and hopes.
It doesn't take. The snake's charge hits, she braces for impact, and...
It doesn't hit? Instead she notices a dizzying sensation and suddenly the air feels very different from the dusty cave air.