I'm not sure why INZ refused you a Work Permit under the Partnership Policy and gave you a Visit Visa instead.
You can get a Work Permit if you have skills that NZ wants, you are suitably qualified and also have a job offer. I'm not clear what kind of certificate you have from Thailand. I think INZ is looking more for people who have a degree from a university rather than just a certificate and those who have more work experience than 4 months. Have a look on
here to check whether you think you could apply for a WP.
One alternative if you want to work while you are in NZ and you are 30 years old or less, is to apply for a
Working Holiday Visa . You would only be able to work for some of the time on this visa because it is mainly meant to be for holidaying in NZ but it might give you long enough in the country to qualify for your 12 months with your partner.