I wouldn't mention it either. She will probably do the sniff test the next time she brings her child to daycare and remembers that she hasn't smelled smoke in your home. If she mentions it, tell her what you stated here and emphasis the "in the evening" part. If she asks if you have ever smoked during daycare hours, in a friendly manner, look her in the eye, and tell her never. She may just need to be reassured....if she asks at all.