I am deeply sorry for your loss. Your Mom sounds really awesome, and this sort of passphrase is really smart.
But, "proof" of God's existence in this way would eliminate the need for faith. Conversely, you also cannot prove that God does not exist, making it a faith, of a sort, in both directions.
Truly, faith is a choice: you choose if you are going to have it (or try to have it), or not.
And thus not having faith is also a choice -- it's an implicit, and sometimes explicit, rejection of faith; and, thus, God.
So I wouldn't hold my breath waiting for that message from your Ma, as awesome as she sounds; if she is wrong, and there is no heaven, then you will never receive that message; and, if she is right, as I deeply and humbly believe, you will also never receive the message because that would eliminate the need for you to make a decision, personally, to have faith or not.
But, "proof" of God's existence in this way would eliminate the need for faith. Conversely, you also cannot prove that God does not exist, making it a faith, of a sort, in both directions.
Truly, faith is a choice: you choose if you are going to have it (or try to have it), or not.
And thus not having faith is also a choice -- it's an implicit, and sometimes explicit, rejection of faith; and, thus, God.
So I wouldn't hold my breath waiting for that message from your Ma, as awesome as she sounds; if she is wrong, and there is no heaven, then you will never receive that message; and, if she is right, as I deeply and humbly believe, you will also never receive the message because that would eliminate the need for you to make a decision, personally, to have faith or not.