Cathy was the fill-in female lead for the Skyliners for the period between Janet Vogel and Donna Groom
there isn't any Cathy in either of hsm1 or hsm2. however, there is a Cathy in the stage version of HSM. She is one of The Thespians and is described as a little too eager.
Yes there are photos of them.
Photos of Buddy Holly with Maria appear in several of his bios.
None that I have found.
yes