I'm really sorry to hear about what has been happening. I apologise for saying something that may be painful to hear, but I'm afraid it sounds like your mum has got into the habit of minimising things because this isn't really the first time he's hit her, and it's already a pattern of abuse - slapping is hitting and throwing plates is violent.

However, I think that's not a conversation to have with your mum because it's good that she's told someone - though very difficult given you're her child and now you're being put in the middle of it. I think it's worth emphasising that she's not overreacting by getting checked out, that's really important to do. I would tell her that she did the right thing saying something.

People like this don't change without proper professional help and unfortunately a couples therapist is not the person to provide that.

I think you do need to let your mum decide for herself what to do, but provide her with the tools to make that decision - does that make sense? I would give her the number for a women's charity, as you say mum not mom I wonder if you're in the UK, in which case Women's Aid - the key national charity working to end domestic violence against women and children are extremely helpful. They will listen, can help advise her and will not judge or push her to do anything. I would also recommend the book Why Does He Do That? by Lundy Bancroft.