To answer your question about a safe spray - Melaleuca.com has Sol U Mel - Melaleluca oil in a water soluble form - does not hurt anything and lice hate it.
The oil is often referred to as Tea Tree Oil - but the true pharmaceutical grade is not always what you find on the store shelf.
And most Tea Tree Oil shampoos don't have very much of the oil in them. Melaleuca has Melaleuca Original Shampoo with lots of the oil in it - we used that for treatment and prevention when we thought we had been near lice.
Spraying the head with the Sol U Mel or massaging the scalp with the oil and wrapping it in a hot wet towel for 10 minutes causes the eggs to burst. Repeating that ever other day for a total of five treatments would be really good. Then spraying anything in the house with the Sol U Mel was our method.