I know you’re joking, but she wasn’t 18 yet before they changed the picture.

AFAICT, kids own the copyright to things they create[0], but guardians are responsible and can use it on the child’s interest. IANAL, consult an attorney, etc., etc.

0 - https://www.copyright.gov/help/faq/faq-who.html#:~:text=Can%....

Completely off-topic, but this other FAQ at your link is so interesting:

> Can I register a diary I found in my grandmother's attic?

> You can register copyright in the diary only if you own the rights to the work, for example, by will or by inheritance. Copyright is the right of the author of the work or the author's heirs or assignees, not of the one who only owns or possesses the physical work itself.

It makes complete sense, but I imagine it also means important historical documents can go unpublished, if they are discovered after the death of the author.