Well, if V1 doesn't have any great tactical skill that we don't know about, then the OP's argument that V3 should have handled the Anati invasion and V1 the Earth infestation is a very good one. Explanations like that she did display some high space-battle tactical skills throughout her career but not narrated in Visser is also possible.
In any case, I would say 'mistake' or not, that she was successful with in preparing the battle in the Anati system but betrayed by the counsel. The sentence of to both her and V3 of "Death by Kandrana, but you can earn a pardon by performing well" allows them to still be useful to the counsel, but allows the counsel to dispose of them anytime they are no longer useful (or more potentially dangerous than useful). V1 wondered whether Garoff (her mentor) acting as the speaker for the counsel would be good or bad for her, possibly because Garoff knew her level of ambition well; so stringing her along just as long as she was useful then using the criminal excuse to get rid of her as a threat.
So the scenario in my mind:
The counsel passed its judgment at the end of Visser. This got V1 into the Anati system, where she devised the attack on the Anati homeworld which involved laying a brilliant hidden trap of Dracon cannons amid the asteroid fields, so that should the Andalites come to the Anati aid, they would be wiped out in an ambush (maybe it wasn't that brilliant of a plan and anyone else leading the battle could have done it just as easily, in which cause V1 was sent there just to provide more authority and get her considerable personal troops and ships into the area).
Then, someone among the counsel (Garoff? The Emperor?) or the counsel as a whole betrayed her, deciding to carry out the Kandrana starvation even though she had set up a good battle plan and clever ambush. A further sign that this was a personal, malicious act is that rather than having the starvation carried out in the Anati system where V1 already was, or bringing her before the counsel to execute her before her superiors, they bring her before not only someone inferior to her rank but her personal enemy to make the execution personally humiliating.
We know that it wasn't an actual failure in the Anati system on V1's part (which is what Taylor seemed to believe in #42, The Test) that caused her to be executed, because in #46, The Deception, when the Animorphs contact the Andalite fleet they have information from Marco's mom that V1 had set up the ambush and that the Andalites would be wiped out if they got caught in the trap.
The irony is that if V1 set up a battle plan and ambush that would have been successful, then was removed from power and sentenced to execution by the counsel, then the counsel inadvertently provided the Animorphs with the info from Marco's mom to save the Andalites from the ambush.
