When she is not angry, have her practice a few techniques. When she initially feels the angry rises, she takes a step back and closes her eyes for 10 seconds, counting to her self. You may have to catch her and tell her 'step back and close your eyes'. You may have to do this repeatedly until she recognizes the build up.
Another one is to put your tongue on the roof or your mouth, breath in for 7 seconds, hold for seven seconds and out through the mouth for seven second- eyes closed.