Like Karrie mentioned, some schools do have rules governing extra-curricular activities (i.e. morality clauses etc) that appear to be fairly arbitrary.
Tangental local incident incoming. My wife was telling me about how kids in a local high school here have been kicked off the football team and cheer leading squad because of a "sexting" incident where a couple teens sent naughty pics of themselves back and forth. Because they are minors (and the DA likes persecuting teens for this type of stupid experimentation, rather than concentrating on real crime), charges may be forthcoming but at this point they haven't been laid... but that didn't stop the admins from booting some of these kids from the activities.
The whole idea seems half-baked to me, but I can see how these clauses appeal to some people (the hall monitor types). My issue is if you're going to do this, have some REAL justification; don't boot/suspend kids until charges are laid because you don't know what they have done until that point. Back to the OP, I don't know if a lawyer will be able to do anything in this case, but its patently ridiculous that some busy-body would want to punish this girl for possibly stopping a friend from committing a serious crime (impaired driving) and endangering lives. Whats next? Punishing kids because you don't like the color of shirt they are wearing or the friends they have?