You've got this right.
Both the
Ranger's ability and the ability of
Crown of Crazy direct you to "Use when one of your Monsters is squished." and are Interrupts. They also have a cost of zapping your Hero card. If you cannot pay the cost, you cannot use that ability.
Ooh, Shiny! will allow you to Unzap your Hero card, but since it isn't an interrupt, the action of squishing the monster must be resolved first, so it has already been moved to the discard pile.