When you say she's in her A frame, is it in the coop with the others, so they can see her, get near her, without actually being able to get to her to hurt her? A dog crate, or sectioning off an area with chicken wire works good for this. After several days, let her loose with them, while you are standing far enough to observe, but close enough to intervene.
There WILL be a bit of fighting. It's called pecking order. Allow it to go on for a minute, as each hen challenges her, shoo them, after a minute, BUT break it up immediately if there is blood drawn. Try it again later that day, OR the next day. Pay attention. Often, if there is a problem, it will be with only 1 or 2 of the top hens. Grab the bully (or two), and put them in the cage, or partitioned area for about 4 days, then reintroduce them. IF the bully(ies) have not settled down some, put them back in isolation for a couple more days. Rinse, repeat.
Isolating the bully(ies), breaks up the dynamics, and when repeated isolation is needed, they figure out that the bullying will land them in isolation.