How long does it take to get a 1-year visa after receiving a work permit in Thailand?

Which is no longer available except for Shareholders / Directors of Companies

Yes, JD, this is correct IF she needs a One Year Extension of Stay.

But she mentioned 1 year visa so I suppose she meant Multiple Entries Non Immigrant B Visa (sticker on passport) based on work permit.

Okay - situation - you have the 90 day B Visa - you have your WP. In the last 45 days (some offices insist on last 30) you apply for the One Year Extension of Stay. This can take one or two meetings close together (depending if there are any deficiencies). Then there is a 30 day wait for the Extension Application goes to higher headquarters (usually Bkk) - for Shareholder / Director of a company - during this 30 days there is a visit by an I/O to inspect / check out the business and take a photo of the employees.

In short the One Year Extension is stamped in 30 days after the Application is submitted.

With the work permit request, you are able to get a Single Entry (90 days) visa.

Once got it, your work permit will be ready (after no more than 30 days) and you can apply the 1 year visa; by the way usually it is applied once the 90 days are going to expire.