Apparently nipple confusion can be an issue but both my boys had dummies from a few days old with no probs with BFing. Like Helle said, the cherry shaped ones are recommended.
I managed without a dummy with my DD (she's now 8 months old) and from a long term point of view I do prefer no dummy to dummy - it is hard to wean them (sometimes) and they can go through a stage where they lose them during the night and you have to keep getting up to stick it back in. Some say a dummy is better than a thumb and I agree - DS2 started thumb sucking when his dummy was taken away (at 6 months of age) and he is now 3 and still sucks his thumb.
One thing to keep in mind with very young bubs is that they spend ALOT of time at the boob. It's not unusual for a 1 week old to feed or suckle for 2-3 hours at a go. They just suckle, and suckle and suckle! This is ok - it is all about establishing your milk and getting her to know you and vice versa. So if you find yourself on the couch from 7pm to 9pm with her, then up again from 11pm to 12am, then again at 3am to 4am, she is probably perfectly normal and wanting to suckle you rather than sleep. I am not saying this to paint an awful picture or anything, but just to reassure you that suckling and wanting to be with mum all the time is normal newborn behaviour.
But all that said, you do whatever it takes to get you through - if right now, a dummy makes your life easier and she takes it, and you get to sleep for a few hours when you really need it, then give it a go. Provided you keep up the BF and don't let her suck the dummy instead of you, you should be ok You won't be the first mummy to try it in desperation at 4 in the morning