I only wish that there was a way of answering your questions without doing an assessment on your sister... but I am afraid that there really isn't, and the value of the answers, if I tried to give them, wouldn't be all that great based only on an email conversation.
Wellbutrin (bupropion) is typically prescribed as an antidepressant. It is less often prescribed for anxiety.
Klonopin (clonazepam) is often prescribed as a medication for anxiety.
I would just add one other thing, from personal experience I know that trying to help family members with mental health issues is a very tricky thing. You should, of course, encourage your sister to get the very best help that she can, and reassure her that you care for her no less because she has had anxiety problems.
Has your sister tried psychotherapy? This may help her work through her underlying issues which are creating the anxiety.