I haven't any experience with 8 year olds either, but talking to the school counsellor sounds like a good idea. I also like the idea of you going out with her too. However I think it important that maybe you swap with Tim, I think she needs to spend time with him too especially if her attitude is directed at or because of him iykwim? I think if you are the one constantly taking her out it will divide you all iykwim? You and Matilda, Tim and Coco. Maybe family outings that she has chosen would be a good idea too.