How does it work? Throwing a marble is not like a die...does it count where it touches the table for the first time?
No, if you're really good (or lucky) and you manage to make it land onto the target, it deals damage like a regular die.
However, if you aim for the target holes, that still counts as a hit (and is much easier to achieve). It deals no damage, but it triggers her rather powerful special effects (that do not rely on the power icon, since marbles don't have faces, and thus are much easier to activate.