I dont think I can answer all of your questions, but for sure some.

As far as skin to skin contact and getting an std, its the area of the skin that has the std that has to worry. If a guy has genital herpes and your vagina touched him there or had contact, then you could get it. But if ur arm touched his arm your not gonna get it that way.

Another issue is through blood or bodily fluids contact. If she has herpes in her mouth and drank from a cup and then you drank from it and happened to have a sore in your mouth or something then again its possible that you could get the std but other than that it is unlikely thought you should be carefully because things like fever blisters etc are contagious. If your so worried, just dont drink after her.

How old are you? If you are so worried you could always get tested but im pretty sure you are not going to have an std with what you have described in this post. As far as katie, your sisters friend, im not sure what the ethical or right thing to do in her situation is. But again its unlikely that she would transfer anything to you or your sisters baby.

the herpes you have on your mouth is not a sexually transmitted disease.

Genital herpes is a different strain of the herpes virus.

Many young children and adults alike have cold sores (that's the herpes on your mouth).

Actually a doctor has told me before at like school presentations that if a guy had genital herpes and a girl went down on him, she could get the form of genital herpes in her mouth...

Genital herpes are on the genitals - the clue is in the name.
If a girl went down on a guy who had an outbreak of herpes, then yes, she could pick up the herpes virus if he has hsv-1 but not if he has hsv-2.

Hsv-1 is the cold sore type of herpes - this can affect the genitalia and the lips.
Hsv-2 is gential herpes.

You can not get genital herpes by sharing a cup - you could get a cold sore if the other person has a cold sore at that time.

Of course, if you have a cold sore and go down on someone, there's a possibility that you could give them genital herpes. But it's quite slim.

At least, this is according to my nursing professor. I don't know her source, but I do trust her implicitly.