I was trying to help a student on how to do a cartwheel. She is 15. I demonstrated and tried to break it up for her but she is just not getting it.

Any pointers for how to teach a basic cartwheel.

i'd check out youtube.
some vids i saw had mats with hand and feet prints on them
most older people tend to be afraid to get their legs vertical
i'd have her pracice with feet a little in front of the line, hands on the line at first to get the feeling, then work on getting them into a straight line (ill try to show below)

hand hand
foot foot

A common mistake in performing a cartwheel is to go sideways into the movement. You should actually rotate the body through a sideways position in the middle of the cartwheel.

Break down, facing the side, one foot infront of the other, reach down and out to place the hands, as the back leg lifts off the floor. The hips come up the head must relax down and the 2nd leg lifts off the floor. You hit the middle of the cartwheel where your body is facing straight front, legs in a wide 2nd position, then as the leading leg comes to the floor, your hips should naturally rotate so that you end up standing in the same position that you started in with one leg infront of the other but facing the opposite side.

This is a technically correct gymnastics cartwheel. It's also a lot less scary to get into, reaching the arms overhead or swinging sideways into a cartwheel can feel very out of control and scary.

Doing the movement properly, the student should feel totally in control, infact you can have her do it step by step like slow motion. It takes a lot of strength but allows the student to feel each part of the movement.