Doesn't sound like mothering or playing to me either, at least not in way humans typically think of it (e.g., nurturing, patient, gentle). It sounds more like an adult dog schooling (bullying?) a puppy that the adult views as problematic --- for whatever reason. I wouldn't allow it to continue for several reasons. First, YOU are the one who should decide what's appropriate/inappropriate and shape/correct behavior of one or both, as needed. Some adult dogs are good at parenting unrelated puppies, others not so much. Second, there's the size differential which can quickly injure the puppy (physically and emotionally). Third, that size differential isn't going to last forever and as the puppy grows up, you may have a really serious problem on your hands. Stop it now.
I'd do as others have suggested and keep them separated (crated or leashed), as necessary. I'd also make it VERY clear to the adult female that her behavior is not acceptable and correct it as needed. That means that, even if you have her leashed, you still have to monitor and correct her behavior (e.g., hard stares) before she acts. The message to her is "I'm in charge of both of you and you don't get to do that or anything like it." And, you have to be utterly consistent with that message.
I've always typically lived with 2 dogs, though I'm down to one at the moment. My approach has always been that while I'd prefer that they develop a good bond with each other, I'll accept peaceful co-existence (that is, ignoring each other). I set the rules and I enforce them because I'm in charge (or pack leader, alpha, whatever you want to call it). That means that I step in and correct (even harshly, if needed) when anyone breaks the rules. For example, I don't allow rough-housing inside and only what I deem appropriate physical play outside. No exceptions.
Last edited by Aly; 07-28-2019 at 08:21 AM.