Thanks for the reply Blossoming, I thought you might like to hear the end of the story.....
After much research, I went ahead and bought a Joy For All Tabby cat- Amazon £113 + 12 spare C size batteries, even though the 'sleep mode' means that the batteries last quite a while, I didn't want her to have a problem. I've put in the correct size screwdriver for the battery compartment too.
Cassie the cat (her new name) looked so cute in the box and the batteries were all ready fitted so it was very easy to set up. There was also a brush included for grooming.
Seeing the smile on my sister's face (a Big soppy grin actually) meant it was well worth the money. 