That is far too painless. You are right that she should wait until he is asleep. Then double stitch sew the sheets to the mattress. When she finishes sewing the sheets all around the circumference of the mattress and no escape is possible she should wake her husband up by hitting him over the head with a baseball bat. He literally won't know what hit him. Then she can proceed to beat him to death. She will have no trouble hitting him. As he flails away and tries to escape his head will be clearly outlined and she can continue to deliver dozens of fatal blows to the head. As his bloody pulp nears unconsciousness she can explain why she is doing this. She should then proceed to breaking his legs, arms and rib cage. This will intensify his awareness. She can then at her leisure deliver the final coup de grace -- another 50 blows to the head. She should then mail pictures of his bloody carcass to his male friends telling them they had better sleep with one eye open. Then she better find a place to hide.
Sounds like too much work. The shovel to the windpipe method is quick 'n' easy.
But well deserved.