ISO: jello layer cake like grannie's

My grandmother made a sponge cake that had jello poured on it and was iced with cool whip. I can't find one like it on the internet. It was not a single 9x13 it was 3 layers and each layer had a different flavor jello. I'm wondering if mixing the jello with a cup of hot water, letting it cool and pouring it on each layer would work. My concern is that if 1 cup of the mixture is enough for a 9x13, is one cup going to be too much for a single layer? I hope this makes sense to you all. If someone makes a cake like this, I would appreciate the recipe very much. My mother wants to make one and we can't find granny's recipe in her cards. Thanx so much for any help.