This time last year, I adopted two nine-month-old Leghorns, Lucy and Ethel. We lost Ethel to predation in April. I was devistated. Lucy, however, didn't make a big deal of it at first. She just clucked along, trying to keep her established schedule which included a fair bit of casually supervised time roaming around in the main backyard. It was only after about a week of being mostly confined to her run that I felt like Lucy really knew Ethel was gone. Of course, I have no way of knowing what was really going on in her bird brain.
I do know that she wanted little to do with me before we lost Ethel. After the first week, she started trying to warm up to me. It was several more days before she started persuing me for companionship. If there had been someone taking care of her for the first 10 days, I don't think she would have noticed it wasn't me feeding her.
My guess is that she will be fine alone for a few days as long as someone checks on her daily. If she's anything like Lucy was, she'll want to be your bestie when you get home from your trip.
Of course, this is all anecdotal and your hen may respond differently because of the age difference between our birds. I don't know. Either way, I wouldn't subject her to a coop-mate until you return. If you have the accommodations and a substitute carer, you could go ahead and get a couple or more hens into your quarantine program while you're away. I would get more than one, though.
I feel like this long response offered little in the way of help. I apologize for that. Condolences on both of your recent losses.