Congrats, Ivy!
You collect the correct number of gems and put them in a special box from the KC store. Then use the menu on the box to redeem them for your cat. The one you get is random...
http://kittycats.biz/fancies-cats.htm
I saw them from L$3999 to around $7500 the other day at Too Adorable, and have mine set at L$5000 in world and L$5275 on the MP due to the fees. (I'm happy to sell it in world for L$5000 - just IM me.) I recently sold one on the MP for L$5250.
