1) Many if not all Helpers will say they attend church on Sundays. This is not true and not to be too cynical but many are trained to lie or "put their best foot forward". They are not as innocent as they seem. Even with day to day requests they will usually come up with some "reasonable" excuse rather than give the full truth. This is not to say they are bad people. It's just the an observation after dealing with many helper situations on my own and through my extended family.

2) your helper probably is relatively new to using the Internet and porn can be tempting for anyone. I agree with some posters that it could eventually become a problem or even an addiction. Personally I think you should address it directly and tell her the real reason why the computer is running so slowly. If you decide it is her own business what she does after hours you should definitely keep an close eye on how well she is doing her job and that she is not slacking off to go play on the computer.

3) managing employees has a parallel to bringing up children. You have to respect their individuality but they need to be reign in once in a while and be reminded of what is reasonable behavior.