I wrote down White WASC but at the time I was experimenting with box mix WASC and scratch mix.  Do you think there is that much difference that she will notice?  I document everything served at a tasting and the recipe used, but for some reason didn't for this cake.

When is this cake due ? Maybe you can email/call her and just say you wanted to re-confirm all of the details ... ? 

Since both are really called White Almond Sour Cream - she wouldn't know what ingredients I used in it.  I'm just going to go with scratch which I prefer and hope she is happy.  There is a difference to me, but I doubt the customer will know any different.  Keeping fingers crossed. 

That little voice in the back of my head just keeps saying;

LET THAT BE A LESSON TO YOU.......

AOr you could send her samples of each and let her choose. It's better to err on the side of caution and honesty. Better to correct the screw up now than to mess up on the wedding cake.