This paints a great picture, thank you. You're not arguing whether she deserves it, but whether the law actually ties the two together properly. My point here however was to not only fix the algorithms but the laws too. Idealistic, I know.
(As you've not described these ideals, just asserted them, is the rationale religious in nature?)
The fact that jurisdictions as varied as California, Illinois, most other US states, Spain, & much of the EU don't yet do that is evidence to me that any "idealistic" case driving such a determination mustn't be too widely held.
And many couples prefer the separate treatment that's allowed them by current law. (Can you imagine the rage from a DHH-type, in mirror-universe where he and his wife had worked to maintain separate finances, but the law clipped his credit based on her income & repayment history? It'd be pretty similar!)
Finally, even if the laws of every jurisdiction, from towns to the UN, required such a link – it still wouldn't be identically costly/profitable to lend to each spouse of a pair, or equivalently costly/easy to collect in difficult situations.
Married partners don't become identical in earning power, conscientiousness, concern about their credit-rating, profitability, etc by either the act of marriage or any legislative fiat by people who wish that might be so.
In matters of the heart, sure, defer to romantics who see marriage as a total, unquestionable unification of two people into one eternal unit. In actuarial matters of lifetime probability and credit risk, defer to the people who have the real data & money on-the-line: creditors.