Does a character with the Sentinel feat whose opportunity attack hits an enemy, forced to move by Dissonant Whispers, have to stop the enemy?

Question

The first benefit of the Sentinel feat (PHB, p. 169-170) says:

• When you hit a creature with an opportunity attack, the creature’s speed becomes 0 for the rest of the turn.

Situation: A Bard stands behind a Fighter. The Fighter has the Sentinel feat.

The Fighter is battling an enemy in a five-foot-wide corridor.
The Bard casts Dissonant Whispers and the Enemy fails their saving throw.
The Fighter has not yet used a reaction, and executes an Opportunity Attack(OA) as the enemy leaves the adjacent square using the enemy's own movement.
The OA hits.

Does the enemy:

1. stop running away?
2. keep running away?
3. run away or stop at the Fighter's option?

I think that the answer is (1), but are there rulings or errata, or Sage Advice that provides the Fighter the option to not stop the enemy on a hit with that OA?

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Notes:

<sub>1. Attribution for the three images: they are tokens of a D&D 5e NPC noble, a drow fighter, and an efreet from the Roll20 compendium. I think this is fair use. If not, please advise and I'll change the images.
2. I was somewhat surprised to not see a question on the interaction of this spell and this feat</sub>

Answer 1

It stops the enemy.

Dissonant Whispers states that

On a failed save, it takes 3d6 psychic damage and must immediately use its reaction , if available, to move as far as its speed allows away from you.

Therefore, if the Fighter hits,

the creature’s speed becomes 0 for the rest of the turn.

And so the enemy can no longer run away. Notice how the text doesn't claim something like "You can cause the creature's speed to become 0". Just like Dissonant Whispers must make the enemy run away, the Sentinel Opportunity Attack must stop the target. By RaW, the Fighter has to decide what is more valuable, for the enemy to back away from whoever it is running from, or to do the Opportunity Attack damage.

That being said, I don't think it would be broken to allow the Sentinel user to determine whether the enemy should be stopped in its tracks or not. At my table, I would allow the Fighter to attack without stopping the enemy. Results may vary.