What you are doing is good. I would keep her separate for 4 to 6 weeks (quarantine) to make sure there are no hidden health issues you could pass to your other birds, and in the meantime get her healthy again. I'd give vitamins and electrolites, and use veterycin on any wounds til they heal. Go slow integrating her into your flock. Since she was bullied before she may be very timid again and be low on the pecking order. I would put her in a parallel run if possible, or a section of run fenced off, for a while so everyone can see everyone, but no one can touch. Then start letting them in together, supervised, for gradually increasing periods.
If you have another bird that is pretty docile you can try putting them together so she's not all alone, but supervise to make sure it works. When no one seems to care much anymore, you can move her into the flock full time.