Toni, I'm sorry that you are having to worry so much for your sister and that she is going through so much. Though I don't have a huge amount of advice, I thought I would share what worked/works for me.
I have always been very phobic when it comes to medical procedures and tests of any kind. I refused to see a doctor or dentist for years once I left home and had no one forcing me to go. I worried about the things you listed-about the procedure itself, whether something would be found and I had little trust for doctors (I still don't have a lot of trust in that area). I don't know why I feel the way I do, I didn't have any major medical dramas as a child but for some reason I have always been neurotically afraid of this.
Fast forward and DH & I had been trying unsuccessfully to have a baby; the next step was fertility evaluations. It took all of my willpower to just get in the door of the clinic and I was shaking by the time the dr finished explaining tests, treatment options, etc. We left and I told DH I wasn't ready to undergo something like that. But eventually we went back because I really did want to be a mom . . .
It was tough. The only way I could get through it was to focus on one thing at a time. One appointment. One blood draw. One injection. I just tried to get through each one, one step at a time. After each thing, I would start crying with relief that it was done (usually on the way to the car-I always managed to hold it together in front of others!). DH was exasperated but I just couldn't help it. I worried constantly about the next thing on the list until it was done. It kept me up at night.
Ultimately, though, my breaking it down one step at a time, it started to become smaller and the smaller pieces started to become less of an issue. When you have a list of medical tests, procedures, and evaluations that you have to get done, it's just too much, it's overwhelming, it's scary, you feel like you don't have control. It makes you feel like not doing any of it. (Also, I do think doctors order too many tests sometimes . . . but that's another discussion.)
Anyway, so if your sister has similar fears or issues (which it sounds like she might given the info in your post), maybe it would help if she had someone to orchestrate the whole thing for her. Does she have a friend or relative that could do this? Someone that could talk to her doctor and find out what are the crucial things she needs to do, what are the steps and what is the most important that she do. And is there anything she really doesn't need right now? Or that can wait? Then she can maybe start from there . . . or maybe that person could make the appointments for her and not worry her with a list of everything she has to do? If she can get through them one step at a time without having to focus on everything, it may help. Plus, sometimes researching a procedure online can help too (it can also make things worse though so be cautious with this!).
I am dealing with a different medical issue now and I am taking my own advice and trying not to worry about the big picture and just focus on each thing, one at a time. I purposefully do not let myself think about what happens if the next test comes back abnormal too. I'm not at that point yet and it just makes it harder for me to do what I need to do right now.
I wish you the best. I have always felt bad for my DH, who has literally walked me emotionally through every single medical procedure I have had since we got married. Not sure if I could have done any of them without his care and support (the first time I went back to the dentist had me on edge for weeks prior!). Not everyone would be so willing to tolerate this stuff as he is. It's a difficult position to be in and I don't envy you for having that role.
Jen
PS-Ultimately, after going step by step through many many blood tests, ultrasounds, countless injections and other tests, procedures, etc. for 6 cycles, we still did not get pregnant. Next step was IVF and I thought there was no way I could ever handle that (go under anesthesia?!?!? are they crazy???). We adopted instead. Took a break from it all. After adopting our son, we returned for one more fertility go round and did another couple of cycles before agreeing to try IVF. I had myself under SO MUCH STRESS through that IVF process, it's a wonder we actually managed to do it. I am very proud of myself for getting through it-I never would have thought I could do something like that before. Dh almost cancelled that IVF about 10 different times. I'm so glad he didn't, our beautiful daughter is worth every minute of what we went through to have her.