Can you direct a controlled mount to ready a dash action?

Question

So you're a ranged combatant riding a controlled mount, maybe a horse. Regarding "Controlling a Mount", the PHB states about controlled mounts:

It moves as you direct it, and it has only three action options: Dash, Disengage, and Dodge. (PHB, p. 198)

Can you direct the mount to ready the Dash action (maybe on the trigger "whenever an enemy comes within 10 ft. of us, move away"), or is this prohibited by RAW since Ready is its own action?

Additional: As a DM, would you allow it, or would this make your job of challenging the players too difficult?

Answer 1

No

Readying something requires taking the Ready action:

Sometimes you want to get the jump on a foe or wait for a particular circumstance before you act. To do so, you can take the Ready action on your turn, which lets you act using your reaction before the start of your next turn.

Since it's not in the "Dash, Disengage, and Dodge" list, you can't direct the mount to ready anything (unless it's acting independently, but that's a completely different story)

Strictly speaking, readying a dash action is not a thing in 5e. You "move up to your speed" in response to the trigger instead. The action is still Ready, not Dash.