I can't comment much on aplastic anemia. my understanding is your bone marrow was damaged from your leukemia treatment when you were younger and your doctors now want to reboot your bone marrow with your sister's donor stem cells?
I had a stem cell transplant when I was 32 for something different, a rare bone marrow cancer called multiple myeloma. I am pretty much back to normal now, but my cancer is in remission, not cured, so I will likely have another stem cell transplant in the future ( MM is a chronic cancer)
In the present time peripheral blood stem cell transplant has mostly replaced the older bone marrow transplant procedure, though we still call it “bone marrow transplant”, it is much easier.
Your sister is given a medication to stimulate her body to make extra stem cells; these are then collecting in a process similar to donating blood so she is not put under or anything.
A transplant is more or less the same procedure, doesn't matter what they are treating.
You will have a central line into your chest, (done with a procedure with local anesthetic). This allows for you to get medications and for blood to be drawn for the lab. You will be given a large dose of chemo, and then you get the stem cells back a few days later. That is the whole “transplant”. Then the waiting begins for them to start making new blood cells. If you had a blood transfusion before it is pretty similar to that.
Many of the side effects are from the chemo (you loose your hair, nausea, mouth sores, diarhea) Then as you are waiting for the stem cells to start building up your immune system you have to be really careful about getting an infection (visitors must wear a mask, not come to the hospital sick) you will be on a special diet at the hospital (no raw fruits, no salad etc) and probably get frequent meds and fluids through the central line. There is a lot of blood work, and frequent vital sign checks for fever or blood pressure issue.
I was able to be my own donor so I do not have to take the anti rejection drugs / steroids. I was really sick for a few weeks while I was in the hospital, but the nurses and doctors are there to look after you. If you develop a symptom like nausea they have a lot of meds they can give you to try and deal with that. The worse issue for me was the chemo irritated my kidney so it would not work properly so I had to have a lot of fluids all the time to deal with low blood pressure.
I think it is important to ask your doctor to explain the procedure to you, ask about what ‘chemo’ you will be given, the side effects to expect, what you will need to do in your recovery etc. etc. Knowledge is power and it will help you feel empowered if you are involved in your own care, making decision etc. You were still considered a child when you had Leukemia so you will probably now be treated more like an adult and it is different. I have heard that from other young adult cancer patients I am friends with who moved from the Children’s hospital for treatment to our region’s adult cancer centre.