Spouse and I funding expenses differently

In asset setup we have 3 RIA accounts: Hers, mine, ours. Hers has a lot of money in it, the other two have less. We both also have two tax-deferred accounts each. Spouse and I are both retired, not yet collecting SS. We share expenses equally. I contribute to shared expense cash pool monthly via cash distributions from my IRA. She contributes via cash from her regular investment account (post-tax.) How do I model this in PRC? It seems that the preference is to drain all the RIA funds before dipping into IRA.