Duchenne muscular dystrophy, as you know, is a very serious muscle disorder that affects boys. It causes gradual deterioration in muscle strength, and most boys who are affected with the condition only have a life expectancy into their early 20s, mostly because the condition eventually effects the muscles that are used to keep breathing.
The condition is an X-linked recessive condition, which means that it is passed on the X (female) chromosome. Since boys only have one X chromosome, if they get that chromosome from their mother then they will be affected. Girls, on the other hand, have two X chromosomes, so they generally will not be affected, although they can potentially pass the condition on to their sons. If a women is carrying an X chromosome with the Duchenne gene on it, then their is a 50% chance that their sons will be affected by the condition, depending on which X chromosome they inherit.
I would strongly suggest, given your family's history of this disease, that your daughter consult with a genetic counselor about the possibility. There is genetic testing available for the condition, and it should be possible to determine whether or not she is a carrier for the condition.