Just tell her you will not talk to her while she is yelling. When she is ready to calm down and discuss things calmly, you will be glad to talk to her.
Now, with that being said, when she does try to talk to you, let her finish her thought without interruption and actually listen to what she is saying and not what you think she is saying. If you aren't sure of what her point is ask her to clarify it for you. I realize this may not be what is happening but often this is how things escalate to shouting. If it still doesn't work than communicate through letters.
There are facts left out in your question that might help people. Do you two live together? Apart? How often does this happen, and what do you think is the reason for yelling? Are drugs/alcohol involved? Does she do this when you are alone with her, or in front of others? All I can say is that you're her mother and no one should be yelling at the other. If she has her own home, suggest that she leave until she can control herself. Are you doing something or do you have a habit of irritating her? Then stop it. If you two live together, decide if you want to continue living like this, or split residences.