It sounds like the Lord has put it on your heart that there's confusion involved in this. It's wrong (as you know) for the other girl to 'joke' to your daughter about why they cannot hang out. Unfortunately, they're young and do not understand what's going on here spiritually - but you do. The concern that I see here is how that 'joke' was used to cause pain and rejection to come on your daughter. Pray to the Lord on how to break that from her. I think it's the right decision to distance them from each other. Don't be concerned about what others think (that's fear of man); be concerned on what the Lord thinks and what He is showing you here. The Lord knows what is going on in the spirit realm with this and the effects of it, if it continues to manifest. I would suggest for you to grow in your understanding of spiritual warfare and learn by the Lord, on how to pray and take authority in the Spirit, for your child. Her heart and soul is more important here. And also, it may be helpful to find a good Christian childrens' book that covers these issues for children - on how to handle them. This could be an opportunity for you to study with your child and review these situations with her, from a Christian standpoint so she can feel strong in her faith and understanding.
Eph. 6:12; 2 Cor. 10:3-4
Lord, I ask that you release Your Holy Spirit in greater power and authority upon Mamato4 and her daughter; that You would impart greater wisdom and understanding of Your ways; you would increase their faith and boldness to walk in the Spirit; that you would break any of the strongholds and plots of the enemy towards this family; and cover them in the blood of Jesus Christ of Nazareth.