My decision would change and I'd tell her to leave Lee, and hope some kind strangers happen upon zombified Lee and put him out of his misery eventually.
I think being forced to repeatedly bash Lee skull with a blunt object would be far too traumatizing for Clem, and she wouldn't be able to recover fast enough. It could lead to her making mistakes that get her killed quickly afterwards.
"It's a natural instinct to fight for our own survival. What makes us human is that we fight for others." -AA:T&T