If my sister did this in a tournament, would it call for a disqualification for her?

One time in Pokemon Stadium 2, I actually defeated her in one of the Challenge Cups Battles with preset Pokemon. I was going toward my goal trying to win, not caring much whether or not she had cute Pokemon and then after her last Pokemon fainted, she immediately switched controllers and I tried to prevent her but she was stronger than me and the controllers ended up being switched to make it look like she defeated me and I lost the match. But God knows I didn't lose that match because I won with my own controller. If my sister did something in a tournament on someone by switching controllers against someone who actually won because all the refs have to do is announce who is going on to the next round if they see someone who won, and if they found out she was lying, wouldn't they have to disqualify her? Because probably, this isn't the first time she would've done something like this. Thinking she should always be the winner when she knows she lost.