Help with introduction behaviour

Hey All,
A little back story first :I have lost two girls in the last week, needless to say its been a rough transition, for me and our girl Joule. She's roughly 2, and is/was? a very timid little girl. I say little because compared to the two who passed she's always been the smallest and the other two acting like her big sister. We noticed she was becoming depressed after one of her cage mates left us, and the other was declining. So we knew she needed some companionship soon.
We got 3 new girls, all sisters around 5 weeks old. We have a double critter nation, and we sectioned off one half for the new ones and Joule in the other. The little ones were very apprehensive about the cage, but not about my hand or my presence, they love being pet and played with, but they wouldn't leave the hut they had taken refuge in. So initially we were going to give them some days before we tried to do too much with them. However, Joule REALLY was not happy about not having free range in her cage, not in an aggressive way but a very sad staring at the stairs i locked up kinda way. So, I decided to bring her up to the girls and see how she reacted, super guarded and ready to abort mission at the smallest sign of anything. Well the exact opposite happened. The little ones all came out and were running around like she was there long lost relative. They jumped all around her, under here etc. They literally went from extreme apprehension of the cage, to totally forgetting they had any fear whatsoever. Joule was super excited, running around with them, smelling them and the cage. Then they all found an area to cuddle, and slept for 3 hours together.
My concern is, they are super small ( for me at least) and Joule will stand on them with her front paws for them to submit ( which they usually do), but occasionally I hear a couple squeaks...which don't sound distressing but not sure if I should be worried. Also, when the little ones climb up the side of the cage, and it really only seems to be the rambunctious one she targets, she grabs them down with her mouth and then places her hand on them. I'm not sure if this is aggressive behavior that I should be very concerned about or mildly, the young ones don't seem to be scared or put off by her behaviour, when i intervene, Joule just stops and they both look at me, then go back to running around or eating...
I have never had girls this young, especially with a 2 year old who seems to just be so much bigger than them I'm worried shes going to accidentally hurt them when I'm not looking.
I haven't left the room there in, because I'm being cautious, and if I do leave Ill remove Joule to be on the safe side.
Holy long winded, sorry, I'm not good at giving information in a small space :s
So should I leave them how they are?, Should I be removing Joule at night and when I leave? Do you think this is maternal/aggressive/confusion behavior... ???

I put this in the wrong area, sorry...I need to work on my forum skills.

Hi and congRATS on the new little ones.

You jumped ahead in your intros which is fine if you have super docile rats. Sounds like things turned out pretty darn good anyways. Joule is doing the right thing, teaching them manners and what's ok and what's not. So she's pinning them and that worries you? Are the little ones on their back when she puts her paws on them or is she mounting them? If she's mounting them, I would probably close off the cage when you are not around to supervise, if she's flipping them and pinning them on their backs, then that's totally normal.

Thanks for the reply Jorats,
Yeah I jumped the gun, but I was 99% sure she was going to react well and 1% that she would run away from them and was on the ready with a towel/ husband for quick extraction. Turned out even better than I had hoped. The pinning worries me only because I don't know how much force she is putting behind it and some of my fears may be due to the fact I've never had such wee ones that im worried shes going to break them. Some times they are on their back, sometimes there on the stomachs. she doesn't mount them per say, and normally i kinda intervene by placing a hand in the cage which usually stops...next time she does it I'll pay close attention to see if its mounting behavior ( there all sleeping again now). The other thing I'm worried about is Joule grabbing them off the side of the cage when they climb. Is this normal? Keep in mind, this is not continuous, I've only seen her do it twice, just not sure why she's doing it.

I should also add, that she has not left the area where the 3 little ones are. She cant sleep where they are because they found a little nest where she cant fit, but she has found the closest possible place to sleep near them, which I assume is a good thing. Earlier she was sleeping on her side, and letting them crawl all over her while she just rested. All good things I presume, and which leads me to believe maybe she is taking a maternal role?? :hug4:

She's being very maternal. The yanking them off and dragging them to her is very motherly.
She sounds like a wonderful rat and the best thing that could of happened to those babies.

Thanks Jorats, for confirming my suspicions! We'll obviously still be guarded and watchful, but it lessens my fears a bit.

I'm so happy for you, DrEllie! It does sound like you've chosen well and are off to a great start with finding new friends for Joule.

I'm learning a lot from reading your questions and jorats' response since I'll be making an introduction or two in the not too distant future, I hope.