I can echo much of what's been said in that there is no way to determine what is causing your sister's symptoms based on a description, and such bumps could really come from a number of things (including those not related to HPV or other STI's). No point in guessing, though, so she should see her healthcare provider to have them sort it out for her.
Family practice doctor/nurse/physician's assistant should be fine, and sometimes city/county health departments sponsor STI clinics. Planned Parenthood, as suggested, is another choice (http://www.ppfa.org
Good luck and post again sometime if you like,