The bodies in the funeral home don't appear to have any trauma to the head, yet they have not turned. The bodies actually were walkers, but someone had applied makeup to restore their appearance. This was evidenced when Daryl wiped away some of the makeup on the cheek of the first body they saw in the funeral home. As for head trauma, morticians can also reconstruct faces and heads, depending on the extent of the damage.
Bob ironically leaves Sasha alone because he wouldn't want Maggie to be alone. Granted both Maggie and Sasha would face the same risks (walkers & other humans) when left alone. All he did was shift the risk.