Metering problem is very common for low end Canon DSLR when shooting people, because they don't provide you with Spot Metering, unless you upgrade to 1D or 5D, or change to other brands of DSLR (Most of other brands DSLR have spot metering for their low end products).
In your case, the best you can do is to use Centre Weight Metering (pointing at the face of the model) and add some EV until you feel satisfied.
Hope it will help you. Happy Shooting.