When one tries or may attempt to harm themselves it is different then for ex a doctor telling an adult family member about your neurological symptoms. When you are suicidal or attempt you are not making good choices mentally and can't often times so why family is brought in and told. I think that the mom needs to find out why she is so mad. Did you friend say why? Her mom is in a very unhealthy right now. When someone is in this type of state it is hard to make the right choices. It is not something she should keep hidden from her family. Part of healing is to face and acknowledge this.
I hope your friend and her mom get into treatment. This impacts the whole family and support is so key. If your friend wants to chat I am here too. It was really hard to face this when similar happened to me with my mom.