Nicole, I'd suggest you first set your camera for the optimum pixels available when you are taking photos in low light. You want the most pixels to play with when you need to 'doctor' the photo. Secondly, the more times you mess with a photo, the more blurry it's going to be. If you resize it, change the lighting, add some more light, resize it again, etc you're compromising the picture quality with each edit you do.
Try either one of these tips. I edit and work with photos and images and jpgs and graphics all day long as a hobby. I've found that if I set my camera for a much higher quality photo when it's darker and I know I'm going to need to edit it, that it will turn out much more sharp. You could also try adjusting the contrast when you are lightening the photo also. Just be wary of overdoing a photo.