@Nick ******
your wife, if over 50 years old, must apply for her own 90-days Non-Imm-O visa. She will need to prove her own financials - 800,000 THB on her bank account (for the visa the account can be anywhere, but for the Extension the account has to be on a Thai bank). She can try to get a "dependent" Non-Imm-O visa, but many Embassies are only willing to issue it if you, as the main applicant, are on a Non-Imm-O/A visa.