The average job in Thailand pays about £300 a Month. In UK its £1,500-2000 a Month. Of course they should pay less. I have Zero issue with it. If you dont like it go somwhere else that has one price for all.....Expensive!
You will struggle. The no. 1 thing they look for is substantial reason to return to Thailand. If she has no job, no property she would struggle in my opinion.