A few more corrections, mostly in the last verse, based on the recording by the Rambos.

MAMA'S TEACHING ANGELS HOW TO SING
(Dottie Rambo)

There's a voice missing in our little country choir
'Rock of Ages' will never sound the same.
God heard her singing, Heaven was not complete,
Now Mama's teaching angels how to sing.

CHORUS
Mama's teaching angels how to sing.
Heaven's halls are silent when Mama sings.
David lays down his harp and Heaven's bells won't ring,
When Mama's teaching angels how to sing.

The old home is empty, it's lonesome since she's gone
And it's hard to know she won't return again.
But I'll meet her in the morning on Heaven's golden hills,
Where Mama's teaching angels how to sing.

https://www.youtube.com/watch?v=lZNzB8nBKCc