Yes, a nine year old dog can still conceive a litter accidentally. While fertility tends to decline with age, it is not uncommon for female dogs to remain fertile until they are 10-12 years old. If your nine year old dog was in heat and came into contact with an intact male dog, there is a chance that she may have become pregnant.
It is important to note that breeding a nine year old dog can be risky, as older dogs are more likely to experience complications during pregnancy and childbirth. If you are concerned about your dog's health, it is best to consult with a veterinarian to discuss the risks and benefits of breeding her.