My mother went in for a fusion on her spine and came out with MRSA and died from it. In this case the cure was worse than the disease.
Infection always has and likely always will be a risk when you open up a human. Evaluating, understanding, and measuring those risks is the only way we can begin to mitigate them.
On the bright side, recent medical technology has also brought us a lot of minimally or non-invasive procedures. Those generally have much lower (sometimes almost zero) risks of infection.
This tragic and inexcusable outcome is doubly so because even a "successful" implantation of a spinal fusion has, essentially, zero chance of improving pain or mobility outcomes[1] and patients would be much better off pursuing a moderate, graduated course of walking-as-physical-therapy.
I'm sorry that your mother died.
[1] https://en.wikipedia.org/wiki/Spinal_fusion#Effectiveness