We got Trooper Thorn from Boxer Rescue LA when he was 10 months old. He was awesome, but we could tell he was a little lonely. We had always intended to get a second boxer, but we wanted to give him some time to bond to us first.
We went back to BRLA and tried to find a companion, but the boxers they brought out to meet Trooper Thorn didn't seem compatible to him (their opinion, not necessarialy ours). They felt that TT was a dominant male and needed a more submissive dog. We thought we would have to get a puppy, but we really wanted to rescue one instead of going to a breeder.
Circumstances arose that we were able to rescue a 2 month old brindle that we named BeBop. Trooper Thorn LOVED him!! I was worried that BeBop would have separation issues from being removed from his litter, and I had rubbed a stuffed animal on his mother and father to give to him to sleep with. HE could not have cared less, he was only whining in his crate becasue he wated to be with his new cool older brother. They bonded immediately and I adore seeing them play and sleep and love on each other. They hate being seperated and I really do dread the day that one of them passes; not just for our sake, but for the one who is left behind.
Anyway, I would contact BRLA (since I see you live in So Ca) and get theri opinion. You can set up a weekend visit where you brink Molley to meet another dog and they will definately gove you good advice on who they think is a good fit or not. They are all about doing what is is EVERYONE'S best interests.