Honestly, I think that if it's your house and your property you can feel completely free to stipulate what it can be used for. The argument could be made that if she's allowed to watch television that pay-per-view porn rented via that source is okay too. If you feel uncomfortable about it you don't need to justify your reason--either here or to her--you just tell her you don't like it and you don't want her to do it. Honestly, I think that's disrespectful use of someone's property--if it is the case that that's what she's using it for. If she really wants to view porn she probably should find her own personal source to do it through (own computer or DVD player). But, I think it depends on what your own standards for your home are. If you're okay with other members in your home doing so then it would be a double standard to not be okay with her doing so. In our home none of us view porn and I think that if our helper was it would be super disrespectful to us. But again, it's what you're comfortable with because it's your home. And that pretty much goes for most things along these lines.