Salary from US

I have read of and know someone who works on a computer in Thailand for an American company. Her income goes into a bank in America - after deductions and tax and is transferred to Thailand periodically.

If you are in Thailand working on a computer abroad you don't pay Thai income tax. Money brought in from abroad is not taxable. If you work in Thailand e.g. sales calls then you need a work permit.

I agree.
If your work does not involve Thailand in any way:

no Thai customers
no calls to Thais that are business related
no meetings in Thailand
no Thai bank account involvement (in other words, your pay is paid to accounts outside Thailand)
then ...

NO WORK PERMIT.

NO need to talk to immigration in any way.
And downright MASSIVELY STUPID to do so.

Otherwise (see list above), you are working illegally in Thailand and need to structure yourself to work legally. If it is a branch office, a major headache.

Thaiquila ain't no legal expert.

If you are working (whether earning income or not, and regardless of where the money is) and you are on Thai soil doing it, you must legally have a work permit. Whether or not you can get away without having one is another matter.

Thaiquila ain't no legal expert.

If you are working (whether earning income or not, and regardless of where the money is) and you are on Thai soil doing it, you must legally have a work permit. Whether or not you can get away without having one is another matter.

No, I am not a legal expert.
I wish I had the link, but I read a very clear and explicit item from a THAI IMMIGRATION WEB SITE which clearly stated it was totally OK to work in your Thai home earning money abroad, no work permit necessary, and that indeed it was WELCOME because you were a good farang spending your hard currency in Thailand.
I still contend it would verge on the insane to try to get a work permit for such a situation. Totally impractical too.