Bobbi she is absolutely BEAUTIFUL!!! I can see why she stole your heart!
Patience, patience, and more patience is all I can suggest. Make sure you give Briggs as much attention as possible so that she knows she is still tops in your book. Sometimes this takes what feels like forever! Sammy had been our only cat for several years when Leroy came along. He hid for weeks, wouldn't have anything to do with us and absolutley hated Leroy! After three months of running from a room everytime Leroy walked in he decided to stand his ground. They worked out the pecking order and Sammy has been confident in his Alpha role ever since.
I wouldn't give Lydia lots of attention in front of Briggs just yet. Whenever that gorgeous Briggs is around I would make a fuss over her and let her know that she is still loved. The rest, unfortunately, has to be worked out by them.
They will eventually come to some type of terms. They could turn out to be snuggle buddies or they could end up just tolerating each other. You can't predict the future with these little buggars!!

We always teased you about Briggs matching your furniture and curtains so now you are going to have to do a room in black and white!
Good luck and keep us posted on how things are going. You have two very gorgeous girls!

I'm so glad to see you back!