I souls go for the 17-55 for your camera, it looks nice, has fast af, has good re-sale value. But, sigma's new17-50 2.8 os macro does it all better. When I was in Italy, I ran into a shop that lets you rent lenses. I've been needing to replace my 18-55 and it was on sale, so I gave it a go. Really nice, really sharp even wide open, great os. But everyone knows sigma has sketchy os so make sure you get a good copy, but also, the rumors are the same for the canon 17-55's is. And I know the sigma has great af speed, (almost canon fast, but faster than the tamron 24-70.
The tamron is slower but decent for what your doing. However, if you are going to sit right up in her face to play and take pictures, you'll only get som headshots with a bit of distortion. Both the sigma and the canon handle that. So the 17-50/55 focal range is best for you, you just have to weigh which lens will have a better chance of being a good copy.
(probably the sigma)