A.F.
Hi D. :-0
Hmmmmmmm... the first thing that struck me is the apparently drastic changes in this child's behavior.. it sounds as if there is some kind of crisis going on and a reaction to it. Since this mom and you have always been good friends, you should be able to speak with her, setting up a private time for the two of you to discuss what you are observing. You can let your daughter know that you are going to set up this time, so that she can occupy her friend's attention to give both parents some private time.
Hopefully during this time together you will be able to share your observations with your friend about her daughter's changes in behavior. You can represent your daughter, with her permission, in saying that she is feeling uncomfortable because of how their relationship has changed and is not mutually supportive anymore. At this point, the hope is that this will open the door for further discussion with your friend who may well be aware of a single or multiple crisis that have occurred.
As a single parent, the mom may not be aware of any crises or may not be so aware of these changes in behavior. Sometime when children reach out for help and can't find it, they resort to "self medication" to find solutions. This self medication can take on many forms. Extreme acting out can be one of them, you just never know what is going on at home.
Be as open and as supportive as you can be, but remember that your primary concern is yourself and your family/daughter. Your daughter is not comfortable with this young friend anymore and so you need to think of her and your family first on how best to meet those needs, and then your friend and her daughter, second.
Blessings on your journey!
hugs,
A. R.N., Energy Medicine Practitioner