Just google "Boat US Boaters License", pick a state, take the online quiz and print out your "license" (which they may call a "Certificate of Completion", but it looks really OFFICIAL!) Easy, peasey.
Be sure to use the "Boat US" site as it is free - the others all charge, if you're naive enough to pay.
It is accepted all over the world, if, as is almost always NOT the case, you are asked for your "license" or "proof of competency" or whatever. (I used it once, can't recall which country.)
No need whatsoever to get your USCG six-pack license or take any ($$) commercial "competency" or "sail master" or whatever course for a "certificate". Only the Brits get their knickers in a bunch over formal Yacht Master stuff, VHF certifications, etc. etc. KISS.
Better yet, don't let Iris out of your sight!
Re: Insurance - Pantaenius issues a so-called "Blue Card" that states your insurance coverage in multiple languages and is welcomed everywhere (and sometimes required) - I suspect other carriers have a similar document. It's kind of like an "International Driver's License" which is not a license at all, but just a document translating your US driver's license into many languages. Good to have and inexpensive at any AAA office.
Cheers and hugs to Iris,
Craig - SN68 Sangaris - Tropic Isle Harbor, FL