She needs to have a job, 25kbht/month will get you a 1M5bht mortgage.
No credit history required, just 6 months wage slips.
No job = no mortgage.
My misses owed 500kbht, taken to court, not allowed to own anything for 5 years then debt written off. 2 weeks after the debt was written off she got a 1M5bht mortgage using forged pay slips (no job) ......... so I don't think credit history is even considered in Thailand.
Be aware,
She may be deliberately sabotaging the mortgage application in the hope you'll be daft enough to pay cash. Mine certainly tried that until she realised no mortgage = no house purchase.