new puppy and older dog play

Question
We have a 14 1/2 y.o Aussie (Koko), which we have had since puppyhhood,
and an approx. 5 y.o border collie (Bella) which we adopted from the shelter
three years ago.  A few days ago we adopted another dog, a 6 week old
border collie/lab mix, Pearl. My main concern is how we socialize Pearl with
the other dogs.  We introduced them slowly and Bella and Pearl seem to be
getting along well --- I think Bella is quite happy to have a playmate.  Koko
pretty much just sticks to her own space and has not been too receptive with
the new puppy, but they have had very limited contact so far.  My concern is
mostly with Bella and Pearl.  I watch them like a hawk when they are together
--- the puppy is so young and small, I am not sure how much and what kind
of play are acceptable with these dogs.  They both will do the play bow and
hop around each other --- the puppy nips at Bella quite a bit, and Bella has
responded with mostly rolling the puppy  around with her muzzle or head,
some mouthing, and a lot of jumping around.  Is this normal and OK?  I have
no intention of letting them have completely unsupervised time together for a
good  while, just wondering if I need to curtail the current play, etc.  (I have
put a stop to play a few times when the puppy has bitten hard enough to
make Bella yelp, Bella has not acted aggressively after these incidents, but
has ramped up the play enough that it just seemed too physically rough for
such a small puppy.
Thanks for any advice or input you would have!

Answer
Hi Susie;
Sounds like everything is peachy to me.
Koko is a senior lady, and is a little too old to keep up with a young pup's energy, so she just stays on the sidelines.
That play sounds ok to me.
Bella, being a Border Collie is a natural protector.
If she yelps, and the puppy get too rough. Bella may make an aggressive noise, bark, growl that will scare the daylights out of you. She will correct the puppy herself, and she will train it to play nicely.
When we got our little Max. He is Lhasa, and he was about 6 weks old. Our 1 yr old Australian Shepherd, male, took over the puppy like he was it's mother.
Silky, our English Setter, was 5 then, and she was full of energy, but she didn't take to a brat kid. When the puppy had been here a couple of weeks, and Rowdy had been pampering him, I heard a vicious kill sound, but very high pitched.
I went into the living room, and that puppy was hanging from Rowdy's cheek, shaking his head, and acting like Kill, kill.
Rowdy was just sitting there looking at me like " do you believe this?"
I plucked the puppy off and proceeded to scold him and , Rowdy took him away from me, and sheltered him like "How DARE you scold my baby".
A couple weeks later, Max tried it with Silky, and she covered almost the whole puppy with her mouth and made the most awful growl.yell.bark that you ever heard.
She didn't lay a tooth on Max, but she scared that puppy out of his wits, and he NEVER tried anything with Silky again.
We lost her last year at 13 years old.
As long as there is not blood drawn, let Bella raise that kid.
You could scold him for being too rough, but if he nips hard enough to make her yelp, but not bleed, then she is not hurt, and it sounds like she doesn'y mind.
When the puppy gets too rough, bet she will spank it like dogs spank their kids.
When Max was about 5 years old ( and every one in a while still acted nasty to Rowdy) Rowdy had enough, and took Max by the scruff of his neck and threw him across a 15 ft. long room.
We have a 5 year old Sheltie, and he and Max and Rowdy romp all the time. Max is 8 now, and has slowed down some, but Rowdy is 9, and he hasn't slowed down or shown any sign of aging except, he has a lot of grey hair. They are indoor dogs, and sometimes run through the house in a romp, and you shouldn't get in the wauy, you could get mowed down.
If Bella was going to hurt the puppy, she would be avoiding it and showing other signs she doesn't like it there. Her nature makes her a watcher and care giver. Her being a female makes her even more protective.
She probably thinks mom and dad brought the puppy for her.LOL
Charlotte