AIBU mother shouting in my face?

[Nightwish]

My mother is a bit of a funny one.

I had to have a kidney ultrasound so she had DS for me, almost 3 years old.
She only had him around half an hour as I drove up to hers straight after my scan.
DS is a bit grumpy and in a not listening mood today, as 3 year olds sometimes are.
After having a bit of lunch and just sitting around talking to mum and my DBro's girlfriend mum decided she was going off to watch the news.

DS said he needed a wee, then started playing up once he was on the toilet.
I was trying to calm him down, knowing once he stopped shouting and listened he would go to the toilet, after a few mins my mum comes back out of the living room saying she shouldn't need to listen to DS shouting or screaming and to take him off the toilet.
I calmly explained that he had asked for the toilet and I was waiting for him to calm down so he would go to the toilet, and said I will bring him out once he is done. So she starts shouting at me, and I said he is my son, I will do things the way I believe I should and then shut the toilet door.

Then my mum decided to open the door and shout in my face that it was her house, I asked her to stop shouting so she shouting even louder, literally at the top of her voice, lent over me and grabbed DS off the toilet, walking off with him.
He looked worried and was holding his arms out for me so I told her to give him back to me.
So I took him and she stormed off shouting at me to leave her house.

I packed up our things and came home.

AIBU to think shouting at me full on in the face in front of my son is not acceptable? No matter if she thinks she is in the right.

I was so shocked at her shouting so loud at me and DS that I actually wanted to cry, sounds a bit sad I know, but I didn't give her that satisfaction.

She has done something not so different recently, but her excuses are always that she is tired, and my dad always stands up for her saying she doesn't mean it.
It doesn't bother me if she doesn't want to look after DS, I can arrange other things, but I can quite honestly say I don't even want to go up there and see her anymore.

Just to clarify, I don't mean that being menopausal is an excuse in that, it doesn't make you less responsible for your own bad behaviour... just wondered if she was in a permanently enraged state.... just sounded familiar

As I mentioned earlier in the thread she has been like it for a long time.
We all have DS's cold he nicely passed around as kids do so she is feeling ill, which was the excuse my dad gave.

I haven't lived with her since DS was 3 months old because living under the same roof was awful, we actually went to stay with DP's mum until we got a house and have had our own place to rent for nearly 2 years now.

I just don't know if I should accept the apology as her genuinely being sorry, which she is for shouting I'm sure but I know she feels her reasons were right.

I made it clear to her on the phone that if she wanted me to listen to her and do everything she tells me, which she probably classes as respecting her, then she needs to change the way she behaves as that is the reason I don't. I do not see why her way is always the correct way, especially when it involves my DS, it is how I see fit not her.

She has had two serious horse accidents, at 16 then again in 2000. And she does have brain damage, but how long do I just do what everyone else does and carry on as normal every time she flips out.