Wow, how exciting for you and your mom! Getting a Yorkie is such an amazing experience! I'd love to get another one, but I have two already, lol.
I have some advice for when they meet each other... take them for a walk. When your dad drops off your mom, meet them outside and either drive to a park or wherever you can walk them together. Dogs don't walk with their enemies, so they will like the dog they are walking with. After an half hour walk, simply walk them into your home. If you drove to a park, keep their leashes on and walk them into the house, just like you were walking at the park.
They will accept each other much more quickly this way. Also, take away all Callie's toys and introduce them slowly. Start with the least interesting toys and end with the toys that Callie loves most. If there are any tense moments between the two Yorkies (staring at each other, etc.), just get up and walk away. This breaks the tension and because they will probably follow you, they will forget about the issue.
I hope that helps! Enjoy your mom's new teapot
(I have a teapot too and I love it: so much more to love!)