Typically dogs are spayed at 6 months old, so 8 months is fine.
Unless you plan on breeding her, you should definitely have her spayed. On average, dogs who have been spayed live 2 entire years longer than those who have not been. They are not at risk for many types of cancer anymore, and have fewer health complications as a whole.
In addition, you eliminate the risk of her accidentally becoming pregnant. If she did, you would have to deal with the puppies. There are already so many unwanted dogs in the world, there really shouldn't be more.