[Help] How can I help my puppy and grown dog get along

I have a 1 1/2 old 55 pound mutt. Two weeks ago I got a 13 pound three month old puppy. They mostly get along. They like to play together, and they often seek each other out.Sometimes the puppy will snarl and snap at the big dog. This usually happens if Big dog is trying to do something the little one doesn't like. Such as take a toy, play when she is tired, or share a bed. Puppy will steal Big dogs toys and snap at her when she tries to take them back.Now, I expected some quarreling between them. My concern is that Big dog is very passive and always backs down. Even when puppy is nipping at her legs and belly (in play) she doesn't do much besides run away. The only time Big dog makes puppy back off is when puppy tries to steal her kong, and even then it is a grumble more than a growl.Is this healthy boundary setting behavior? Does Big dog have to set boundaries or can I do it for her?I don't want Big Dog to be bullied by puppy for the rest of her life. via /r/dogs http://ift.tt/2qHe4ov