"Somehow there was a mysterious $4300+ payment on (husband's)student loans which paid off all but two of them. Where did that come from? Blessing from paying tithing?"
LOL, I wouldn't take that for granted! A truly moral person would inquire about it.
If it is an accounting error, it WILL be found out and fixed, and they will be back on the hook for payments due. In fact for not reporting/asking about this discrepancy, I've heard of others made to pay late fees and interest and such that would have been owed in the meantime after the unexpected "windfall" was deposited.
When we were in school, we would receive "blessings from paying tithing" straight from "God." Only our "God" was my nevermo dad who had plenty of money to help us out when things got tight, having not paid tithing in his life. We never asked, but sometimes he'd notice and send us over a little something. Interesting, that the biggest blessings came from the person in my life least interested in Mormonism.