Sorry not to catch you in time for your class yesterday

but here's something you might want to do. Find a story board (comic strip?), that is, a series of pictures that tells a story. A good one might be "For Better or For Worse". You could take a week's worth of them to do this activity.
Ask students to combine information from two pictures into one sentence using a relative clause. For example, in one picture, April might be playing with the dog. In another, April might be practicing with her rock band.
Ask the class: Which girl was playing with the dog?
The students answer (in writing or orally): The girl who plays in a rock band was playing with her dog.
To practice non-restrictive clauses: April, who plays in a rock band, was playing with her dog.
For more examples of story-based grammar practice (with listening), visit my website,
www.englishzoom.com By the way, there is practice with relative clauses there, but with a different story, a political scandal.
Best of luck with CELTA!