There are four reasons why a cheerleader wouldn't throw her pass, and each of the four should be handled in different ways:
1. He/she has a mental block- Try and build up the confidence. I have always been an extremely mental tumbler. I know first hand that any type of punishment would not help. Pep talks and repetition are the only two things that help me.
2. He/she is lazy- If I coached I would not put an athlete in a corner for not throwing because they were tired. If they just 'didn't feel like it' or were tired I would make them condition right after they didn't throw and do it again.
3. He/she is injured- This is obvious, but if the athlete doesn't throw because they are injured they just need to sit out or do what they can safely do. The only problem is the athletes that are always injured and the ones who don't tell you and just cry after practice to their parents (which was me). I would never tell my coaches. A good coach should be able to usually tell the difference though.
4. He/she can't (lack of power, messed up at the beginning of a mixi pass, etc.)- Sometimes if an athlete messes up at the beginning of a long pass it wouldn't be safe to throw the end. Punishing the athlete won't help, and making him/her sit in a corner definitely won't. Fix what ever the problem is that they are messing up on.
By "balk" I assume you mean number one or two. No amount of punishment can help a true mental block. In fact, it makes it worse. For number two, CONDITIONING and make them do it. A time out when I'm tired sounds good!