While that deck will certainly have pulled many copies of This Town Ain't Big Enough out of circulation, by itself it isn't the main reason for this spike
I don't think her winning percentages were out of line with her amount of play
While the card can be frustrating to play against, especially when you dont have a removal spell for it, I am still a fan of the card as it breaks the mould of yet another Ragavan, Nimble Pilferer/Lurrus of the Dream-Den deck
What makes this so good is that you only need a dork of a power four or more to work, so every Commander with it should toss this in, as welk as in ones that pump your Commander's power like auras, equipment or Voltron
Zombies boast a variety of lords including prominent examples like Lord of the Undead for card advantage and Undead Warchief for cost reduction
This cycle could be repeated at the end of an opponents turn so long as you had enough mana to pay for it, effectively creating a near-infinite source of 1/1 fliers and a ton of healing