@jgiovann It's natural to be nervous but from what I have seen and heard, complications are few and far between. Pain control is fairly well managed considering that opioids are so conservatively administered these days. There have been studies that have found ibuprofen to be just about as effective as opioids too, so if you can take them you will be fine.
Also, I think hospitals often suggest a longer stay time than typical, just in case it is needed.
Regarding the possibility of your mother rejecting the new kidney, if it did happen please remember that you at least tried by being part of a paired donor exchange. I admire you for being there for your mother, and I am sure she must appreciate it tremendously. My daughter wanted to do that for me but things did not work out.
I think if a person has a rejection that the person goes to the top of the list for a new organ, but I may not be right with that. You could ask about that at the transplant center.
JK

Complications can happen and I completely understand being nervous about.
I had complete faith in the medical side of things. All of the tests you had were to determine not only how well you would live the rest of your life with 1 kidney but how you would do in and after surgery. The very cynical side of me says that not only is this a very expensive surgery but the surgeon and the hospital have a reputation to uphold and would not do it if they didn't think the outcome would be positive for you and your mom.
I am great at avoiding thinking about scary things and worried instead about having time to clean out my furnace filter and fridge before I left. I did want to know the real deal about surgery, before and after so I talked with people on here and also found a "donor buddy" because I had a hard time finding (non medical) info from the donor perspective.
http://livingdonorsonline.org/living-donor-buddies/living-kidney-donor-buddies/
I don't know if you read the very beginning of my "journey" but I was 50, not a marathon runner or even a regular at the gym and could only find stories about those guys donating and I wanted to talk to someone more like me. My donor buddy was a lot more like me than someone doing decathlons.
I had laparoscopic surgery so only have the one incision. I don't know if what goes into the surgeon's decision to do it that way but it seems like a good question. Do you have a social worker from the hospital? Mine worked as a go between for all of the different departments and could either answer questions or direct me to the answer.
As for pain, I had an injection into my abdomen before they stitched me up which lasted 24 hours and of course had pain meds in my IV and to take orally while I was in the hospital. I left with a prescription for 10 days of pain meds and extra strength Tylenol. I think I took the pain meds on schedule for a couple of days and then only at night after that, I took the tylenol mid day or as needed for about a week. I was not being strong or tough, it didn't actually hurt enough for more than Tylenol.
As @contentandwell said, hospitals err on the side of caution and pick the longest times they'd expect you to stay. I was told 2 nights but passed all of my checkpoints so left early. They encouraged me to stay 1 more night if I would be more comfortable.
Keep asking questions and talking about it! As you probably noticed, there isn't much out there from the donor side and the more donors and potential donors searching and finding information, the better!

Part one of my reply was so long I thought I would do this separately.
Most of the people here are recipients and would be better able to answer question about how your mom will fare. I met the woman I donated to the day before surgery so I can't give you too much back story. She was 60, had been on dialysis for almost 5 years and had acquired diabetes and gout along the way. She couldn't walk more than a block without resting and was only urinating once a day.
The kidney started working immediately and her gout disappeared quickly. She is able to manage her diabetes through diet now. She was walking around the day after surgery and left the hospital after 4 nights. She was able to walk the 5 blocks to our hotel. She had to stick around for about a month (she lives 5 hours from the hospital) for appointments.
She had some minor signs of rejection in the 1st year but has been able to drastically reduce hers meds since then and is not showing any signs of rejection. I think she still goes in for labs about once a month and to the doctor every 6 months.
We talk every week and don't go into much medical detail but she is doing well and decided to go back to work because she was getting bored! Since her surgery, we have gone to Mexico for her oldest daughter's wedding, she was at the hospital for the birth of her daughter in law and son's baby.and is helping plan her youngest daughter's wedding. She is very active and I love hearing about her adventures.
Organ donation is truly a miraculous thing and I'm so glad when someone can be a part of it.