Here is the situation that came up:
Player 1 controls a creature enchanted with Ordeal of Heliod and two +1/+1 counters. On Player 2's turn, they cast Portent of Betrayal to take control of the creature, and then attack with it. The attack triggers the Ordeal, putting another +1/+1 counter on it. Now that it has three counters, it is sacrificed and a player gains 10 life.
Which player sacrifices the enchantment and gains 10 life? The controller of the creature (Player 2) or the player who cast the enchantment (Player 1)?