I'm so sorry. It's never an easy thing to do, even if you know it is for the best.
Rest in peace sweet Sasha. My condolences to you & your family.

When it's time to add a new addition you'll know it. You'll never replace her but you can help fill that void in your heart & share the love with another dog. My suggestion is if you think you're ready (or when you are) visit some local shelters. I'm sure that will help your decision, especially if you find the one there.