Can my Filipina girlfriend obtain a dependent visa if we are not married?

An American expat over 50 and his Filipina girlfriend, who is under 50, are inquiring about visa options as they plan to stay in Thailand indefinitely. They arrived using a visa exemption and intend to apply for a 30-day extension followed by a 90-day Non-O visa based on retirement. The expat wonders if his girlfriend can obtain a 'dependent' visa despite their unmarried status, but responses indicate that she cannot, as dependent visas are only available to legally married couples.