OP - It sounds as though you are asking for an evaluation of whether your undocumented niece may get caught traveling to/from HI, not whether she needs more than a California DL to travel.

The answer to the question you posed is that all she needs is a piece of ID acceptable to TSA. That would include her DL.

The unasked question, if it is what you really want to get to is that nobody here can evaluate the chances that she doesn't get caught. But, you should understand that CBP does spot checks at HNL. The broader issue is that perhaps she should use the money spent on a HI trip for a consultation with an immigration lawyer.