DH and I are friends with another couple who have a DD who is the same age as ours, the DDs are in a dance class together. They are moving in a couple of months and we won't see them as much.
Neither DD are great at sharing so playdates have always needed a lot of supervision, but have improved as they have both got older, and they have always called each other 'best friends' etc. The other DD has had a major issue with hitting and scratching for a long time, which our friends are aware of, obviously, and there have been occasional incidents of her lashing out at our DD. Interestingly, when they are both in a group of other kids, the other DD will hit our DD but not any of their other friends.
Things escalated a couple of weeks ago when they were over at our house and their DD lashed out at our DD several times, scratching her face. (She also hit her mum several times
). At the dance class following this, our DD was visibly terrified of the other DD, shielding herself from her if the other DD approached her at all. I dealt with it by telling our DD that she was doing the right thing by walking away from the other DD if she thought she was going to hit her, and by saying 'it's not nice to hit me' etc. But today in class it was even worse, and it was really upsetting to see how fearful our DD was of the other girl. Our DD had a long chat with DH about it at bedtime and articulated that she was sad that the other DD frightened her, and wondered why she wanted to hurt her, but she still wanted to be her friend.
The situation will (thankfully!) resolve itself when they move, but I can't ignore the situation at the moment. I feel as though I need to pull DD from the dance class, or come to an arrangement where one of the DDs changes to a different session. And cannot imagine how I will approach this conversation without damaging our friendship with the other couple. But on the other hand I want my DD to be resilient, and feel if I pull our DD I will be teaching her to avoid conflict rather than face challenges. And she loves the dance class, so don't want to pull her altogether. So confused! 
I'm also feeling a little overwhelmed that this parenting lark seems to get harder as they get older, not easier!