How much is a 21+ year old with a CC permit going to charge for her services? Also, if part of the service you are offering has to do with being armed, in most states that puts you into a completely different licensing category. CC permit/license won't cut it. You need to be a licensed armed guard.
Probably about $10-11/ hour. That seems to be the going rate out here. The bigger issue is about liability insurance if the baby sitter shoots someone. I'd have some serious questions to my home owners policy or to whoever I hired about that. You could end up in court for the actions of your contractor.