Introducing New Dog

So I posted on the Daily Dog that we have taken in a Great Pyr foster pup Emerson. He is a love. Just got him today, and he is passed out on the floor by the door, having sniffed every inch of the house.

Of course, the issues I expected to deal with on his arrival are not at all the ones I am confronted with. I was expecting Dizzy, my older, bigger Aussie to take exception to this big oaf we are introducing to the family. I know her in and out had have planned to make our bedroom her "safe zone" and to take her to work with me to make sure her routine and level of attention stays the same. I was NOT expecting Betsy the almost-not-a-puppy to have a problem with him. She has seriously never taken issue with any dog that has not initiated a confrontation (and even then is very diplomatic and usually defuses the situation). I have never seen her lift her lip, be possessive or reactive at all.

So, of course that is what I'm facing now...

We got Emerson home, brought the other two out on leashes and went for a 10 minute walk around the block. They sniffed hellos and then basically ignored each other, which I thought was a good sign. Let them out in the yard for a while, he had a big drink, sniffed everywhere, peed and pooped while the other dogs played with me and ignored him.

But now that we are inside, Betsy is being possessive of me, and attention from anyone, as well as food/chew toys. If I am petting her and he approaches, she lifts her lip and growls. I made the mistake of trying to give out a treat to each dog and she tried to intercept his and he growled and snapped at her (the only time he has reacted/retaliated at all). I fed all three dinner without a problem but could see that it has to be supervised.

Right now my husband took Bets to the dog park, and Dizzy and Emerson are asleep on the floor near me, all peaceful.

Anyway, this is a new side of her. I know how to deal with Diz when she is bratty like that, and can predict it, but little Bets has taken me by surprise.

Advice please? When to step in, when to allow a growl? Should I keep them in separate parts of the house for now?

The crate I thought was big enough for him isn't, so at least for tonight will gate him downstairs and have the other two sleep with us. Will procure a bigger crate tmrw, and will crate him when I am not here. I haven't been crating Betsy when I am out of the house; is it a bad idea to have one dog loose and one crated? Can crate her too if necessary.

I'm sure (I hope) we can work it out, the situation is not playing out like I thought! I was sure she would be thrilled to have a bouncy playmate so she could stop bugging dizzy to chase her all the time.

Here he is with my mom: