The purpose of the joint account is NOT to give her greater flexibility and autonomy (because you were right -- she's not committed to the marriage, so that doesn't fit). It's to give YOU BOTH a fairer contribution to the family's joint expenses.
If her income is commission-based, maybe you come up with a quarterly adjustment -- "I'll pay 90/10, but then you kick in an add'l contribution at the end of each quarter based on your quarterly-to-date commission income, which brings our total quarterly contributions to the family's expenses up to proportional. And since this would be a joint CHECKING account, this would also give you (wife) a debit card for this account, and your own access to cash for day-to-day expenses."
You need to get her OFF of putting things like the kids' clothes and groceries on CREDIT cards. That's insane. All of the family's day-to-day expenses like that should be on the new joint checking account, where you each have a DEBIT card to use.
Greater accountability to each other; fairer contribution by each partner in the family.
