Make a medium length cast and then place a piece of tape on the spool. That way when she casts and back lashes, it only messes up a little bit of line vs. the entire spool.

This too!

Make a long cast before she starts and put a piece of electrical tape on the spool then reel back over the top of it.

I've taught a hundred people how to cast their bait casters. Most folks don't adjust their reels properly to start. Also they don't fill their reel with enough line. This greatly reduces distance. Fill the reel to within 1/16" of full.

As a beginner, tie on a 1/2 oz lure that cuts thru the wind well, like a lipless rattling bait. Now tighten the tension knob under the star drag until the bait falls slowly when in free-spool. Now adjust the centrifugal brakes on the left side of the reel to about 75%. Depending on the reel, you may have to open the side plate of the reel to access the brakes.

Now the important part: Have her hold the rod&reel in front of her and rotate her wrist so the handles of the reel are pointing up. Tell her to rear back & throw the bait up toward the sky. She can take her thumb off the spool altogether when the bait is in the air. The moment she sees the splash she needs to stop the spool. It should go a good distance.

Just remind her, Handles Up-Throw Up.

As she gets more comfortable with the reel, loosen the spool tension a little at a time. Girls get this faster than guys because they listen to what you say better.