From my own experience with dogs. My boys have always been much more mellow and welcoming then the females. The male dogs also bonded to me solidly, lol (which of course I loved). My females have taken longer to warm up to the new pup in the clan...However, that is not the case currently! I have a 12 + male Shih Tzu, and a 6 month old Yorkie...She is DYING to be freinds with Harry, but he's taking longer then I expected to warm up to her. I actually currently have an application in for another rescue Yorkie and requested a female, when one becomes available. I figure I will need another queen to hold her own with Sunni...but the good news is, whatever the combo I have had, they always warm up in the end.
And I definitely think they need a companion, especially if you are working. They are social little critters and when they have each other I feel less guilty when I have to leave.
Progress was finally made last night...after about 4 months...Harry let Sunni cuddle up with him when they were napping
She tried again at bed time, but that was a fail, haha...progress not perfection.