lol I love redwoodtail, she's my favorite (I mostly did this just because Nala mentioned it in the disc server hehehe)
I'm gonna keep how to do it vague in case others would like to figure it out on their own, but you have to talk to Redwood at two certain points of the game (one being during your apprenticeship, another later in the game). If you do it right, you'll see that right before you start the wedding she isn't at her usual spot in the log >:) She'll attack you once you find where she is, and the fight begins! (Hint: She couldn't have gotten that far from Californiaclan in such a short time...what area is close by?)
I warn you all in advance, the fight is ridiculously hard for joke purposes. Have fun grinding!