Sounds like she didn't realise Lao visas are for staying in Laos and that you need a Thai visa to stay in Thailand. If they look the other way on the illegal entry they may still charge 60 days' overstay on a presumed 30-day visa exempt entry, before she goes on to approach to Lao authorities.
...must have money or "general documents" exchangeable for cash...
เอกสารบรรดา doesn't quite clear the matter up as much as I'd hoped it might. Certainly does apply to traveler's cheques, as we already knew. But as a credit card can be used as a cash advance, does that fall under that category, legally? Again, I'm just speaking in terms of the wording of the regulation. I'm not recommending it.
I didn't say it was about ASEAN treaties, though that is part of what goes throught that office. The government wants all the laws in clear and correct English so that foreigners can have access to and understand the law. This is a big project they are undertaking.
I did a job recently for The Office of The Council of State and was told that with ASEAN they are very serious about having all the laws in correct English. I talked with one of the translators. Again, I understand the actual situation at the checkpoints, but you yourself have mentioned citing the law to officers when they have misstated them. I'm not saying this is a get-out-of-jail-free card, but it should be clarified by the authorities what a "payable document" is.
I'm curious to hear what you find in The Royal Gazette.