Personally Trump doesn't need to make his own daughter an official advisor, clearly she already was unofficially. I personally believe that the only reason he did was because of the buzz that she's the unofficial First Lady, which is hurtful to Melania. So Trump took that off the table.
That said, I can think of two far more egregious cases of nepotism. First, I give you Attorney General Robert Kennedy. Second, I give you Hillary Clinton.
RFK is the REASON why we have the NEPOTISM LAW, now.