You have discovered that just having the gear leaves you a long way away from understanding how to use it all effectively. You need to do more reading.
When using flash the in-camera light meter is essentially useless, because it effectively never see's the flash of light. In TTL mode the camera has the flash unit fire pre-flashes. TTL means Through-The-Lens. The camera senses the light that relfects back into the camera from the pre-flashes. The camera programming that was written by a committee of Japanese camera software engineers then tries to decide what you are trying to make a photo of and what your artistic intent may be.
Often the software gets it wrong.
If the flash in on the camera, and un-modified, the lighting will be harsh and flat. Harsh because the light from a hot shoe flash is apparently to small to provide soft light, and flat because the light is right on the lens axis which kills any sense of depth on the subject.
I wonder what shooting mode you were using?
Using strobed light you don't need a fast lens, because you should have plenty of light that is provoded by the flash unit.
What light was the reflector going to reflect back onto the subject? If I read your post right, you only had one hot shor flash unit, and it was mounted on the camera hot shoe.
To make the light less bright on her when jusing TTL you use the Flash Exposure Compensation adjustment.
It is much easier to put the flash unit in manual mode, set to 1/8th power, set the shutter speed to the camera's x-sync speed, set the ISO to 200, set the lens aperture to f/8, focus and shot.
Then look at the photo on the rear LCD. If the subject is to bright or to dark you can do one of 2 things, open the aperture a stop (f/5.6 for 1 stop brighter, f/11 for 1 stop darker), or change the flash unit power setting 1 stop (1/4 power for 1 stop brighter, 1/16 for 1 stop darker) or a combination of both that add up to 1 stop brighter or 1 stop darker.