by manydills
Here's the timing:-Quest phase begins.
1) Player actions.
2) Commit characters to quest.
-responses
3) Player actions. (I assume here is when you would ready the character.)
It is already step 3. You cannot go back and do something that you needed to do in step 2. Even if a character readies during the response part of step 2, it is still too late.
And yes, if a character is ready when it's time to attack, they may attack. It doesn't matter if they quested or defended earlier in the turn. If they're alive, standing, and their player hasn't already attacked that enemy this turn, they may attack.