I know lying isn't good, but if that's what you have to do to get Zsa-Zsa to the vet then do it. I have a feeling it could be a raptured blood cell in her eye because this happened to my friends dog and it turned out a blood cell exploded. Tell your mom you saw her scratching at her eye or something. I know it's not right but Zsa-zsa needs to see a vet. Instead of lying, maybe you can find some information on the condition/illness or whatever it is and prove that she needs to go to the vets. I got some links:
http://www.northforkanimalhospital.c...s/felv_fiv.htm
http://www.vetinfo.com/cateye.html

I hope they help! Good luck!