Hi Stacey, congratulations on the forthcoming arrival of your baby, life will never be the same, the good news is it will be better. Firstly your babies safety is paramount. Make any introductions short and sweet, associate the baby arriving with good things, such as special treats the dog doesn't normally have, have your mum take her out of the room wanting more. The small child of your cousins IMO should not be allowed to chase the dog, and it is actually a testament to her temperament that she moves out of the way. Obviously babies and small children should never be left on their own with a dog.