If your peace lily pot was wrapped with foil, remove it. Keeping foil around the plant is not good for the long term. Florists wrap the plants with a foil that keeps water from dripping. Good for the memorial service bad for the plant. The foil doesn’t let the plant drain properly.

If foil is not the problem, I would suggest re-potting the peace lily. One, this will help if the plant has been continuously over-watered by giving it a new soil base. Two, it may be root-bound. Once the plant has been re-potted water the plant in and then only water when the soil is dry to the touch. A good way to test if you have properly water is the soil-ball test - performed a day or so after you water.

Pinch some soil from the pot and roll it into a ball. If you can squeeze water from it — too wet.
If you can’t roll in to a ball because the soil is powdery — too dry. If you can form a ball but can squeeze water from it - Your just right.

After a few weeks you should fertilize your peace lily.