What permits and registration does my Thai girlfriend need for starting a beach boot camp in Thailand?

Hello all, I’m asking for some info for my girlfriend who is Thai. She’s a tennis coach already working for a coaching academy but she’s into training also, she wishes to start a ‘beach boot camp’; functional strength and conditioning training in a group environment on the beach.

This would ofcourse be an independent endeavour and she wouldn’t have the comforts of being employed by a company, we’re wondering what needs to be done with regards to declaring the income made and also potential permits required to deliver these sessions on the beach.

I understand this is quite a nuanced question but any help would be appreciated🙏