It is so hard. Your every instinct as a mum is to keep your child safe and protected, and there is that horrible feeling of helplessness when they are being hurt and there is little you can do.
I would definitely not involve any other child's mum. While you are busy getting into a battle or words with another mum, your respective children will have either solved their differences, or moved on, either will be resolved far quicker than the battle you could get into.
When our two oldest girls were gorwing up, we lived next door to a couple who also had daughters of the same ages. We agreed a pack that we would never get into arguments about anything our kids said and did - for the reasons outlined - and it worked out really well. There is little or no future in trying to sort out your child's issues with another parent.
Meanwhile, all you can do is to give your daughter a lot of support - even more than you obiously do now.
She will get through this - and the other traumas that involve childhood into adolescence and adulthood, and hard as it is, you have to let her make her way. There is little practically you can do to help her, except be there and give her lots of love.
My girls are all mums themslves how, and going through the same with their children - it never gets any easier, but it is part of growing up.