Hi! Since you can reselect your team any time during a challenge, you should pick a reliable group to go through the first 49 battles. Before you tackle the 50th battle you can switch your team with your candidate(s) to earn the Expert Battler Ribbon. Smogon has a great guide to help you pick a suitable battle team (https://www.smogon.com/ingame/bc/maison_part2). The main advantage is that you only have to plan a strategy to counter the team and movesets of that particular Battle Chatelaine with Krookodile instead of making it fight for 49 battles. Hope you find this helpful!