I'd expand a bit on Tom's advice. This is an instance where I'd advise thinking long and hard about putting any assets into joint names. The operating checking account (for the electric bill and groceries and the like) should be fine, but I'd keep everything else separate.
Further, if the financially stable person has any health issues or is in a risky profession, the couple should talk to a trust attorney and consider if that person's assets be placed in a trust whose secondary beneficiary is the spouse-to-be, for their benefit but not for their ownership. This gets into legal areas and I'm not giving legal advice - just advice to talk to someone able to give legal advice! Trustee who is not the liened spouse would have to be chosen, perhaps a trigger for wrapping up the trust once the IRS issues are resolved (or not, if the spouse-to-be is still bad with money). It would not be simple or cheap, but possibly less expensive (and peace-of-mind-bringing) than the idea of leaving substantial assets in the hands of one with a track record of making poor choices and bad decisions.