Your basic issue is that you're shooting in low light with a non-IS lens (I'm assuming from the f/1.8 aperture and 50mm focal length that you're shooting with the EF 50mm f/1.8 II on your camera), and using iso 100, even at f/1.8, has pushed your shutter speed down to 1/40s. This is well within the 1/focal_length limits to show camera shake blur from handholding.

The rule of thumb is that your shutter speed needs to be 1/focal_length (in this case 1/50s) or faster to mitigate camera shake blur, but that presupposes good handholding technique, and possibly a lower-res sensor. A lot of folks throw in the crop factor (e.g., 1/1.6x50=> 1/80s), or simply just double (1/100s). IS (such as you have in the EF-S 18-55 IS USM or STM kit lenses) can bring the shutter speed limit back down again, and everybody's personal skillz at keeping the camera steady differ, so remember this is an heuristic ("rule of thumb"), not numbers with absolute certainty of result. :)

Jacob's mom's camera, I'm also assuming had a 50/1.8 II on it, but at iso 1600, the sensor is set to 4 stops higher sensitivity, and can use a shutter speed 16x faster than the one your camera chose (i.e., 1/640s) to get the same exposure, so less camera shake blur.

However, understand, too, that the EF 50mm f/1.8 II's "sweet spot" for sharpness is actually around the f/4-5.6 range. Using it wide open at f/1.8 is using it as its softest and also where it yields the thinnest DoF, and you may be confusing softness or misfocusing with motion blur as well.

See also: Why Are My Photos Not Crisp?