Ask Mr. Smarty Plants

The "closet plant" is also known as the Peace Lily, and its scientific name is Spathyphyllum. As are most indoor plants, the spathyphyllum is non-native to North America, but instead of the tropical Americas and southeastern Asia. It is not, therefore, within our usual range of expertise since the Lady Bird Johnson Wildflower Center focuses on plants native to North America. However, we are always glad to find some websites with the kind of plant care information you need. The most comprehensive one we found on house plants in general, with information about Spathiphyllum as well, is this one from Texas A&M Extension on Indoor Gardening. You may already know that all parts of the plant are toxic, and should not be where children or pets can get to them. If you trim away leaves or divide for propagation, it is recommended that you wear rubber gloves and possibly even goggles and certainly dispose of the cuttings very carefully.

The first fact that we found addressing your problem is that the leaves will droop when the plant needs water. You are probably right that it needed repotting, as it had perhaps pretty well become root bound in the old pot. When you moved it to the new pot, the new soil needed to be thoroughly moistened. A good procedure when repotting is to set the new pot, with the plant and new dirt in it, in a basin of water. Leave it until you can feel moisture on the top of the dirt. After that initial wetting, the soil will accept watering without all the water running out through the drain hole. Another thing this plant likes is to be lightly misted with water a couple times a week. And dust it, you'd be surprised how much dust will accumulate on broad leaves like this, and cut off the light. Take a light cloth, dampen it and wipe the leaves. This plant can be susceptible to poor water quality. If your water is heavily chlorinated, you might consider bottled water. It cannot tolerate direct sunshine, and should be 4 to 6 feet away from a sunny window. On top of all the other reason for droopy leaves, the plant will often droop late in the afternoon, probably from the heat, but it doesn't need water at that point.

Our final thought is your comment that it was an old plant, which could very well mean it has reached the end of its normal lifespan. We have no idea what that lifespan might be, but you might consider dividing the plant and creating some new ones to carry on.