Congratulations on making the decision to donate!
I had questions come up during my journey and called Mayo directly. From what I remember, a nurse/social worker will be the one you talk to initially, so that's who I would try to reach.
I don't know how it works when the recipient is family but Mayo would not give me any info on my recipient including other potential donors or her schedule until it was time for the surgery. Even then, they told me it was based on her surgeon's schedule.
Your sister still probably has a million tests that need to be done before surgery that will take time to schedule and complete. There could also be someone that is already testing as a donor for her. Or the social worker could be busy, which is great if you think about it.
While I was waiting for my full evaluation at Mayo, I got routine medical appointments done to save time in MN. I had a well check, mammogram and colonoscopy, as well as flu and tetanus shots. If you need those anyway, this waiting time is a good chance to get them done.
I had many random non medical questions, so feel free to ask me as I probably asked someone the same thing. Good luck!