Law enforcement best practice is to prioritize the report of sexual violence and not charge the reporting individual with underage drinking as long as they were not putting others in harm’s way (drunk driving, for example).
How family, school, and the community respond will vary depending on values, rules, and policies. Some local jurisdictions have strict hosting laws that may be enforced if your child shares details when reporting, allowing an investigation into the party.
It is always, always encouraged for community to support anyone reporting sexual violence, and you are encouraged to stand by your child if the community response is not supportive. However, it is not wrong for your family and child to take the community response into account when deciding how to proceed after sexual violence. Healing can, and often does, happen in private.