what would be the process for my wife to legally take ownership of my firearms?  Transfer them via FFL?  Or can she simply keep/sell them?

IANAL but my understanding is if you have your will/trust/estate planning documents in order, as long as shes got a FOID and named she can take possession with no FFL involvement.

...(430 ILCS 65/12) (from Ch. 38, par. 83-12)

Sec. 12. The provisions of this Act shall not apply to the passing or transfer of any firearm or firearm ammunition upon the death of the owner thereof to his heir or legatee or to the passing or transfer of any firearm or firearm ammunition incident to any legal proceeding or action until 60 days after such passing or transfer.
(Source: Laws 1967, p. 2600.)...