I don't see where anyone addressed the Most Important consideration = Commingling.
"the source of the AmEx payment will depend on the month, based on which account has the funds to pay so this scenario could happen again."
I recommend you Stop Paying directly from a company that is not the Responsible party for that Debt.
"Since this involves extra work for her she may not want to do this,"
Explain that this opens Both Businesses to scrutiny by the IRS and by any law firm, as well, that wants to "look at the books" and/or Sue. If this person does not want to Respect any separation between these two business, or between Self and Business, no one else respects that, either.
"soas an alterantive I'm looking to see if there is an easy way to make the entries in both company files."
Commingling = you didn't segregate the entries, even if you Tracked them correctly, because paying Amex directly from the entity who is not the Responsible party = Commingled. You want to Move Funds between the entities in anticipation of that shortfall, then let each make their Own Payments.
And nothing here is a Debit=Credit or JE. In QB, you have Tools = an Interface. If this is Desktop, that is Banking menu > Enter Credit Card Charge. For QBO, it is an expense from the Credit card. For Reductions, that is Credit Card Credit, or Return. Or, from Checking, the Credit Card account is the "expense" entry.
If you insist that Company A pays Company's B's debt directly as Loaned to them, that still is Credit Card Credit for B, putting Liabilty as the "expense" reason. And Company A's check "expense" is Other Asset.
No JE should be used.
