From a purely legal perspective, namely, based on what "justice" means in terms of having an actual jury of her peers decide a verdict for Minnie, the answer is "No". Justice was not served the proper way.
This is because the case for Minnie Wright was never really put together the way it should have been in a court of law. Her story was not heard. The tragedy of her life was discovered by accident, and the clues to what caused her to snap were the product of the insightful and intuitive nature of two very good women.
What actually takes place in "A Jury of Her Peers" is an act of providence. Mrs. Hale and Mrs. Peters happen to stumble upon the one piece of evidence that would immediately show Minnie's state of mind, determining that she would have definitely killed John Wright.
Martha Hale's eyes pointed the way to the basket in which was hidden the thing that would make certain the conviction of the other woman--that woman who was not there and yet who had been there with them all through that hour.
We learn that the evidence is concealed and withheld...
from the prying eyes of the men investigating the case and, with this act, Minnie's actual fate may be saved. Whether this was right or wrong is not the question. The question is, whether this would have really helped the situation, or makes it worse if the case were to be still seen in a court of law.
Therefore, true justice is not served in "A Jury of her Peers". It is merely interrupted. We do not know if, by another act of providence, Minnie would have had the right attorney to represent her and explain to a jury how much she suffered, and how she snapped. We do not know how far her case would help influence other women in the same situation. Unfortunately, we do not get that finality that would determine whether justice will, in fact, prevail.