It is very hard, because it is scary and it makes us defensive.
So, we react.. instead of responding.
We want to scare back, or hide. It's hard to think clearly in the heat of the moment.

Choosing to respond rather than react is hard too, takes practice, but feels much better.
It would help you if your mom would give you the time you need to decide on your response. Responses require time and room, to think about what is going on and to think about how we want to respond to it. If she would respect your privacy, it might be helpful if you could tell her you need some time alone and you will talk about it after.