I think I'd be pissed if I was your sister, and you were treating me like a walking biohazard.
You can't get herpes through clothing, and unless your genitals rub up against her genitals long enough to create friction, you aren't ever going to get herpes from her.
You have a lot of questions about STDs and non-sexual risks. If there is no intimate contact with mouths or genitals, these things can't be transmitted.
If you need to (and you may need to), talk to someone about your fear about this (and other germs, if that's a thing, too).