Actually, I think this is a good question. I usually hate the so-called "hypothetical" questions because they are usually just thinly veiled this is really happening questions. So why not give us a little more info. How about some of these for starters:
I realize you "really like and respect" this tica, but do you trust her?
Is she a working girl or a non-pro?
How imminent is your possible untimely demise?
Do you have anyone else to leave your assets or your benefits to?
Do you have any Ch*ldren who would otherwise be eligible for your benefits and how would this effect them?
Do you even have other assets to leave other than your SS benefits?
And how about the much more desirable problem (relatively speaking) of what might happen if you end up not dying for quite some time?
I don't know your possible motivations, but I can guess what they might be. To answer some of the other posters' questions:
Tim, who cares if your dead? EXACTLY! Of course, you don't care. But whomever your beneficiaries or heirs might be certainly would. If you had a choice on the one hand of dying intestate (dying without a legal will) and having all of your estate just go to Uncle Sam or dying without any beneficiaries for all those SS taxes you've been paying your whole life and having it just go back into the pot or, OTOH, enabling some or all of it to go to someone you care about and who probably really needs it, wouldn't you prefer the latter?
NF, why would he want to marry her? If he doesn't have any Ch*ldren and he doesn't have a spouse than presumably no one at all can collect on any of his social security benefits. If he just lived with her she wouldn't be eligible for spousal survivor benefits. This could be a "no-cost" way of seeing that your favorita gets something after you're gone. I'm no expert on SS, so I don't really know the rules beyond the quotes that have been reposted here, but another question I would want to ask a lawyer or the SS is if you have both Ch*ldren and a spouse as heirs does one effect the other in terms of the benefits that they might be entitled to?
TP, to answer your questions of why get married and why not just enjoy (spend?) the rest of your healthy life enjoying it, I would ask why can't one do both? What this is sounding like to me is essentially just a shell marriage set-up for the sole purpose of entitling the tica to a little something after he's gone. There is nothing about that that necessarily precludes Lucky or the hypothetical mongerer whomever that might be from continuing to monger.
Frankly, I'd be much more concerned with the legal questions surrounding that supposedly
rock solid prenup since I think it takes a lot more than just putting it in caps and large font to make it completely "rock solid" (if such a thing is possible) than questions about SS (though the latter is the main precondition for even considering the former). What I have seen is that "rock solid" only covers the stuff that you can imagine but it is the stuff you can't imagine that always seems to get you.