Onychia being an inflammation/infection of the nail matrix, can be prevented like any other problem of this nature by using proper hygiene methods.
If there is a cut in the skin at the base of the nail or if living tissue has been snipped away rather than just the non living cuticle removed then that can leave the matrix open to bacteria and possible infection. This is because the seal protecting the matrix will have been broken. That is why we always as nail technicians take care at this area of the nail.
I am sure if you google Onychia you would find lots of information.
If you know someone who has inflammation surrounding her nail, then before it gets too bad and infected I have found the best remedy to be to submerge it in warm salted water. If there already is an infection then a doctor has to be seen as it will require anti biotics.
HTH