As Trever1t alludes to, you can expose for the face by using Spot metering mode. Partial, or Center-Weighted metering mode might also be used.
I suspect your camera was set to what Canon calls Evaluative metering mode, and Nikon calls Matrix metering mode.
Yes a reflector and/or fill flash would have helped. A key concern is getting light to the eyes, but not so much light that the person starts to squint. An issue I usually have with using available light is a lack of directional control and strength.
To help prevent squinting or blinking, manually controlled flash is the way to go. TTL flash has to use pre-flashes which often causes people to blink.