A lot of folks say that if you keep all males they can do okay, but once you introduce a female they can start fighting each other - this may be true even if they cant physically get to her, just seeing her and knowing shes nearby might set them off to start competing for her if they're ready to start mating. They cant reason "there's no point in us trying to kill each other when neither of us can actually reach her right now anyway." I might be a little bit more worried about the two males having any kind of access near her than her going solo.
when you say you have ducklings on the way, do you mean brand new babies? They're gonna take a while to catch up to your 5mos olds and be safe getting introduced to your drakes when you're ready to reintegrate the whole group, and might not be able to be left with her in the meantime either, depending on how she feels about them. you might have three separate groups for a spell
I think she'd be okay alone for a little while. You dont want to keep a single duck that spends its entire ~10 years of life completely alone but people need to separate their ducks for injuries and illness and whatnot all the time, in the short-term she should be alright (and of course some extra attention from you couldnt hurt)