"Make sure you use the whole arm to strum across all four strings. Don't distort the wrist."
Moving the whole arm under the violin is the best way to take the hand and fingers to each new string. Lead with the elbow and roll the arm smoothly between E and G strings.
The wrist should be in line with the forearm in the lower positions, not pushed out, not collapsed in, and not distorted sideways. This is so that on all strings the fingers keep the same angle in relation to the string.
Try the opposite way - leave the arm at the G-string position and stretch the fingers across to play on the E-string. Feel how uncomfortable this is.
Once arm steering is reliable (that is, the arm will move where needed, when needed), then the movement is often minimal but it's best to begin by exaggerating the action so you are sure the arm is free and available to move when necessary.
Resources - Glossary for Arm steering...