A couple of question about Dis ability, just to be sure I am understanding it correctly. All the below examples will assume you have the fate icon leftover needed to trigger her ability after the test:

1) I attack an enemy with Dis and inflict damage. Can I use her ability before the enemy counterattacks so that I can use a card from the attack test in the negate test of the counterattack?

2) I am attacked by an enemy and test to negate, but the damage/fear I take forces Dis to make a Last Stand. Can I use her ability to put a card from the negate test back on top of her deck so that I can use it in the last stand?

For now I would say Yes to number 1 and No to number 2, but I await clarification.

Well, on the rules it states that the test ends after you "Calculate results". My understanding is that the "effects" of the success/failure of the test are not part of the test but come after the test. So in both cases my answer would be "yes". In any case, before you take a new test, the previous test must have ended already.