I'm playing through Gold using mostly my starter and had a hard time with Whitney. Most people suggest trading for a Machop in Goldenrod and using that. But instead I wanted to use my starter, and when Miltank started the rollout, I switched out to my other mons (all really low level), and I sacrificed the five other weak mons on my team as the Rollout got more powerful. After 5 turns I brought Quilava back out and then won using basic fire attacks. What a fun strat and a way to get past this fight