I don't have Herpes, but my sister does. What can I do to help?

I'm 18 years old, and I'm from Pennsylvania.
My sister is 22, and also from my area.

We don't talk a lot and we never see eye to eye on things, and so I was concerned when she was the one I saw knocking on my door this morning.

Of course I was sleeping, as I most often am before noon on a Sunday, and I was quite curious as to why it would be her. One thought crossed my mind.

She must need money.

Why else would she be knocking at MY door? We haven't even talked for a month, nearly to the day.

Annoyed and somewhat groggy, I answer my door. She seemed distraught, as she usually does when she knocks at my door because of some problem shes facing or what have you.

"Do you have $15 I can borrow?" She asked with a look of discomfort and unease.

I scratched my head and groggily replied, "Uh, I may have $10 or so, is that okay? What do you need it for? How have you been? Everything okay?" I sensed a touch of urgency.

"Anything will help. Can I talk to you for a second outside?" Quietly answered. "Do you have a lighter?"

"Yeah, sure. Hang on a second. Let me get some shorts on and snag my lighter from the stand." I said with enthusiasm.

My roommate was home, and apparently this wasn't a public matter. That seemed to concerned me more, especially because my roommate was merely sleeping.

We stepped outside, the sun was dull, but the air was warm. Rain seemed in the not so distant future. The pavement was warmed beneath my feet. The wind kicked up and the clouds constricted and separated to allow one to notice that the Earth was still at a constant tern.

"Jessica, I just found out I have Herpes. I need the money so I can go to Wal*Mart and get my prescriptions."

I was shocked.
It was so surreal and completely otherworldly.

I never had a problem giving my sister money, I didn't even really care why she needed it. I just wanted to know how her life was, and wondered what irons she had in the fire. Of course, my stomach was churning.

I felt bad for her. Not in a pitying sort of way, but more in a loving manner. How could I help? What can I say to make her feel better about herself? How would I handle the situation if I were in her shoes?

Its hard for me to understand EVERYTHING about my sister. We never get along on anything. Somehow, when one of us needs the other, we sort of manage to set aside our few choice words and help the other the best we can.

What makes this hard for me is that we're not in the least bit close. We share nothing alike aside from DNA, our mom, and a brother. Its hard knowing my sister because she doesn't willingly allow herself to open up to people, not even her family. She has a nasty habit of lying, and sometimes its hard to place your finger on weather or not she is aiming for your attention, or is actually willing to receive help.

I guess my question is this:

How should I feel on this?
What is the right thing for me to do? Obviously I should lend a hand when I can and be supportive, what else really is there for me to do?

I can chose to be safer about my own sexuality, and get tested frequently. I can chose to exist as someone she can lean on.

I guess, I just needed someone to talk to on the subject.

Thanks for listening.