The standard way to do that is with 'git filter-branch'. If your daughter’s email is megatron@example.com,

    git filter-branch --env-filter '
    old_email=megatron@example.com
    new_email=redacted
    if [ "$GIT_COMMITTER_EMAIL" = "$old_email" ] ; then
        export GIT_COMMITTER_EMAIL="$new_email"
    fi
    if [ "$GIT_AUTHOR_EMAIL" = "$old_email" ] ; then
        export GIT_AUTHOR_EMAIL="$new_email"
    fi
    ' -- --all

This is “safe” in the sense that you can go back to the old version with the reflog if you screw things up.