I think that if dunking is all you can get accomplished (due to her being skittish) then dunking is what you do. Not everyone/every chicken can do the soak, scrub, etc. I washed a dirty butt yesterday and wrapped her in a towel and covered her head and she still fought every minute. Hopefully, if you do it more frequently, she'll get used to it and not struggle, but I would do what I could even if it's not the whole routine. I've been dunking mine in an ice cream pail full of mineral oil every few days and it's all I can do to get that done during the week.