There are a several bank credit cards that don't have foreign transaction fees and reimburse. I used my Chase card last summer with Krungsri ATM. Verified I was getting the mid point of their buy/sell rate which was extremely close to the wise rate. It was a very convenient method.
I also paid restaurants and hotels with my credit card. So in addition to essentially the same transaction cost as a wise transfer, I was scoring CC award points that I used for hundreds of dollars back. 😎
If she has entered with her Thai passport before, they have her fingerprints on record. When she tries to enter with her US passport they might flag her fingerprints on file with the Thai passport and question her at that time. Its anyone's guess how they handle her case from there.
Glad you got your 500 baht back. I'd be nervous about any lingering retribution from her or one of her buddies in the future. I.e., if you need anything from that office in the future and you don't have all your i's dotted and t's crossed, I wouldn't expect any sympathy from the officers at that branch.
Does it matter? Even if they don't extend it, wouldn't they just give you the 7 day extension denied stamp which would put you past the Sept 5th departure date.