Can the umbilical cord be damaged by too much licking?

My SBT has just had a puppy and it is healthy and large and both are doing well. The poor thing is being cleaned repeatedly though as the mother has no others to divide her care and attention. I am concerned she will hurt him but also aware she must clean and stimulate so am unsure as to how often she should do this and how rough or persistent should be. Also not sure how to discourage her without interfering with this required behavior ideas or tips for care etc. would be gratefully received the dog and I are both first timers and I want to do the best for them both. Everything else is seemingly good.