"I also wonder if it would help with immediate pain relief if there is no THC in it."
The cannabis used in this product is derived from hemp, which typically has <0.3% THC. According to the company’s reported chemical analysis, one brownie contains 50mg of CBD and 0mg of THC. CBD in general has been shown to be effective in the management of migraine headaches. Usually, the THC levels in CBD products are low enough that psychoactive / intoxicating effects won’t be achieved.
Keep in mind that edibles take much longer than inhaled medicine to reach peak concentrations in the blood plasma; you may want to use vaporized medicine at headache onset to prevent and/or blunt worsening symptoms. Always pay attention to the concentration of cannabis you are consuming in an edible and begin with the lowest dose to evaluate your response to the medicine.