You can probably start by working on her social skills fluency yourselves, since you already have some base skills in this area. All fluency skills are mostly a matter of overlearning. So giving her additional opportunities to rehearse social situations, perhaps practice them in scaffolded settings (e.g., with adults, more skilled children, prepared social partners), will help. She may also have some gaps that can be filled by direct instruction, as so much of social skill development is absorbed informally in everyday interactions. In her case, she may be missing some of the intermediate cause-and-effect steps because of the speed at which situations unfold, or drawing incorrect cause-and-effect conclusions based on incomplete information (for the same reason). Although long-term, obviously one wants her to gain skills for interacting in groups, it may be better for her naturalistic skill development and implementation if she continues to spend significant time in dyads or triads, where she is more likely to be to able catch all the social interaction components quickly and accurately enough to learn and experience success with social skills. Since fluency mainly comes from repetition/practice, and none of us particularly are motivated to practice aversive activities, keeping her social experience as positive as possible will be quite important.
If you're comfortable running through social stories and doing social autopsies with her, those could also be valuable strategies. She doesn't have the same deficits in theory of mind that an ASD learner might have, but she is likely to have some of the same skills deficits--just for other reasons.
