Her son is her all.. She had one child..
She dotes on him, he is her world, comes before anyone.
If you can accept this, then there will be no more hurt, you can't change the way she is, this is the way she feels, sees things and always has..
We accept our family for who they are.
Sure, we can be disappointed, wanting to see a family member but it doesn't happen, she may not be that way, wanting to be close nit, like that, she may be more of a loner these days.
People also change and get very set in their ways as they get older in life.
You have phone/email, be close to her in that regard and never take the non attendances as personal, because I am betting that they are not personal, just her way, now, in her life.