I would say that it is quite possible that she is constipated then ... usually it is only the runny poo that can get passed if she has something blocking her up. Unless it comes out, the poo in her intestines that is not coming out will just get harder and harder.

I don't really know how to deal with constipation in a baby under 6 months, but since it has been going on for a week, I would probably suggest seeing a child health nurse or your GP and see what they suggest. I think it is probably worth getting it checked out. They can often tell by having a little feel of their bellies to see if you need to do anything to remedy it. They would be able to give you the best advice in your circumstance. I am going off a lot of assumptions so I would hate to tell you to treat her for constipation and it turns out that she is not.

Sorry I couldn't be more helpful but because she is so little, I think that you might need some proper medical advice. I hope it gets sorted quickly.