>>53416284gen 2 expert here
1. Accuracy-lowering moves like cyndaquil's Smokescreen and Pidgeotto's Sand Attack are the bane of Whitney's Milktank. unfortunately, they are weak to Rollout so it's a double-edged strategy. without Rollout's snowballing power effect, 70% of Milktank's firepower is gone and all she can do is spam Stomp in vain as she misses over and over again.
2. you can also trade your Drowzee for a Machop on the second last floor of the Goldenrod Department Center. you'll need to level it up first though.
3. lastly, you can tank her with Graveller.
