Coping with Grief and Loss: Advice Needed

I’m needing some advice on how to cope with grief and loss. One of my friends lost her 3 year old son last night. He was playing outside with his friend in the sand of an empty corral at the stables where she teaches vaulting classes. A 25yo guy, out on probation, high on meth, going over 100mph, swerving through traffic and drifting his car around corners with his friends in the car ran off the road. He busted through two steel 5-bar fences and over a buried concrete barricade to the sandy area where his car hit and killed both toddlers instantly. I am struggling with grieving this little boy and feeling guilty because I haven’t kept in touch with my friend very much in the last year or so since our adult lives have become so busy. I’ve known her for 5 years, was in her wedding, was there when her son was born, and we used to be so close. I guess what I’m asking is, how to you grieve when you’re not an immediate family member of the deceased? Especially when the deceased is a murdered child? I’m feeling so many things and I’m feeling all of this guilt for feeling anything at all, like I’m gaslighting myself. I hate having mental illness. Grief is hard enough without it.