Thanks for the suggestions!
We brought the new chinchilla (STILL unnamed as of yet we call her chinnie) out so they could sniff each other with only one set of bars between them.. There was no growling, no screaming, no sounds at all. They sort of appeared to nibble on each others faces, I couldn't tell if they were nibbling or just moving their mouths/noses and they sniffed a lot but nothing either of them seemed to be uncomfortable with.
Being in a busy pet store for 8 or so months with puppies barking and children poking at her through the cage, the new chinchilla isn't too timid and Maggie doesn't seem threatened. I'm hoping for the best.
This is her (she looks much lighter in person).