Mail was supposedly the only method then too. You might want to check your statement unless you've confirmed with the embassy that they no longer offer in person services.
I'd ignore all the suggestions to get a retirement visa. If you're only looking for a 6 month stay, there's no reason to go to the effort - that's for retirees who want to stay at least a year. Also, it requires exchanging/transferring about $30,000CAD or proving you have enough monthly pension income. Really too much work if you're only planning on 6 months.
Right now there's still a visa free 60 day on arrival (can easily extend for another 30 days at any immigration office in Thailand). Normally if you leave to visit another country for a week and then return, you could do that a second time (6 months total). The 60 day is supposed to be going back down to 30 days though, so if that happens then maybe the DTV.
If you have a serious health issue, you have the option to move back to the US and get health insurance via the Healthcare.gov exchange. Anytime of the year, you're eligible to start health insurance that also covers pre-existing and depending on income may get credits to reduce the premiums.
Only risk is an emergency or accidents. Self pay in Asia or an Asia centric plan that could include limited coverage for short trips to US.
*US plans via the exchange start the 1st of the month IF you sign up by the 15th of the previous month so there's a minimum wait of 2 weeks, maximum wait of 6 weeks (if you signed up on the 16th).
Because you must transfer 800k baht to sit in a Thai bank (exchange costs). Interest is almost nothing (or nothing) and if/when you eventually want to transfer it back, there's the hassle (Thailand has stricter transfer out rules), and exchange cost plus rate may/may not be worse.
Keeping that $ in a CD pretty much pays for agent to handle it all for you with no exchange hassles/risks.
If it's a girlfriend, your chances are close to zero unless your gf has strong ties showing she'll return to Thailand (underage children still in Thailand, long term business ownership, etc..).
Also, unless she's very old (40s/50s) then there's the assumption of sex trade.
Best chances are older with ties and applying for tourist reasons with proof of reservations for stay and scheduled tourist activities NOT mentioning coming as a girlfriend.