I know plenty of grad students who have not only brought dogs to graduate school, but who adopted them in graduate school as well. One overarching theme is that the easier it is to commute home, the better it is having a dog - some first-years lived nearby and were able to go home at lunch to let their dog out and such, but other first-years had to miss homework sessions because it took them 45 minutes to go home to let their dog out. That's the major con - finding time to take care of it. Depending on the breed, it might also require a lot of socialization and play time which if you're working 15+ hours a day might be a little tough on time (I'm not telling you anything you don't already know I'm sure!)
That being said, I have yet to hear of a graduate student who regrets having a dog. I know a handful of students who adopted a dog just because it helped keep unhealthy work habits at bay (see: previous comment about working 15+ hour days). It helps with depression, anxiety, and general stress to have a friendly pooch who greets you when you come home!
It really comes down to this: will it make you happy for the dog to be there?
As a side note, I really can't in good faith condone taking your dog to your office unless she is absurdly well-behaved. A dog is distracting, and it's hard to make sure that everyone who is in the office (and/or will enter the office before it is cleaned) isn't allergic. Even if you and your officemates aren't bothered by a barking dog, it's hard to say that the people who are near your office won't be as well.