Ok ... this is coming from experience
I have two littermates
and I have good news and bad news
First the good news
This is normal dog behavior and it will calm down a bit with time
The bad News?
This is normal dog behavior
Dogs whenever they come in contact with another dog
need to have a hierarchy of who's on top and who is second or third
it's not a fairness thing .... and you trying to make it fair will only likely make it worse
Your older dog is exerting her authority when she stops your puppy from barking
Also dog and puppy play is Noisy and sometimes sounds pretty scarey
as long as there are no yelps being heard it's best to leave them alone
What I would watch for and this is something I've had to intervene with
is that the top dog will sometimes horde all the toys and keep the other dog from playing with anything
That is where I and you should come in and place the more passive dog where the alpha cannot reach them and give them some chewy time or time to themselves
va