The training lasted three days, with Alice succeeding in approaching Allura but lacking the damage needed to finish the job. Every time she approached, she would be a step too short or have sacrificed power for speed.
No matter how Alice went about it, she was unable to take the last step needed.
Understanding that there was no use in trying the same thing over and over while expecting different results, Allura opted for a different type of training, one that tested Alice's reaction speed and kinetic vision. She had to practice keeping her Eye activated as long as possible to aid her in battle.
The issue of landing the final blow could be compensated with tools or external help. After all, the Abyss allowed assistance so long as the contribution did not exceed half of the Hunt.