And then get her to work out how many more customers she will need to make the 30,000 baht she lost from the job she gave up.
Get her to calculate the average profit per customer, and the average time spent per customer, and let her work out how many customer hours are needed every month.
In central Bangkok I see prices of 200 baht per hand, so 400 baht per customer. If her business expenses are 10,000 per month and she needs to recoup 30,000 salary then she needs 100 customers per month, or 25 customers per week. If a customer takes 1 hour then she has spent 25 hours of labour already.
If she worked 50 hours per week, and she had a customer every single hour, then she would make an additional 40,000 baht per month - but we all know you are never going to get a customer sat in chair nearly all of the time.
As we all know, she needs to work this out for herself though.