Rosewick

Is there some way to change out the mons in your party right before the fight against Scarlett? Because I'm stuck with an all level 50 party consisting of a Sawsbuck, Scolipede, Toxicroak, Fem Meowstic, Parasect and an Unfezant. I have tried so many times to beat her with this party due to not being able to change them out but I can't beat her, only drop her to one Mon and then it's curtains. Help! Edit: Beat her to a pulp and then convinced her with her bow not to ragequit. I was so happy to actually getting the bow right after getting off the snow mountain because I thought I might find Ava by the fan under the cloud.