I am a first timer visiting Thailand from USA for 15 days, what can I expect to have happen at TSA, Customs? any tips or tricks would be greatly appreciated

My mother will be flying into Thailand via CNX in a few days. This is her first time visiting Thailand and she will be here for 11 days.

If she has proof of hotel booking and exit flight itinerary, how likely is it she'll need 20k baht (or equivalent) in cash at immigration? I know it's better to have it just in case, but she's really anxious about having that much cash on hand while she's traveling.

And, if she does need it and has USD instead of THB, what amount does immigration consider "equivalent"? How exact does it have to be?

Thanks.