Check her story, and the good advice given: How can I give my sister sex-ed?
on how to deal with parents:
- "You might also want to share some of the information and books on sexuality and autism with your parents...Their discomfort with sexuality and them being very conservative about it is going to be an issue, for sure, but it seems possible to at least get on the same page about her safety ...And I'd say that kind of information is what's really critical, anyway, and that you can likely sneak in some pieces about pleasure and identity in that stuff under the radar."
- "I'll be honest and say that I'm not sure how you can really do completely on the down-low, particularly when it comes both to protecting yourself AND not having things your sister says result in your parents freaking out with her, which could obviously impact her negatively. But if that is what you wind up having to do, I'd see if you can't find someone you know will be supportive of your efforts who your parents respect to call on if you wind up caught in the act, as it were, and need some support."
In short: So it sounds like give some info to parents, stress concern about safety, and find a supportive adult that can get their parents ear (or some of it).