So my dad recent sold my childhood home, but before he did, I gathered a few of the lilies of the valley plants we had in our garden for sentimental reasons. I replanted them in a pot as I live in an apartment. They are in indirect sunlight, and I've been watering regularly, and the pot has good drainage. But the leaves are turning brown. I know that in the outdoors, the plants always died in the fall and reemerged in the spring, but I was hoping indoors they would be alive all year round. Any advice?
It is normal for Lily of the Valley leaves to go brown and die back. Both outdoors as you suggest and indoors.
The indoor plants too will revive in spring if kept cool and moist. They need to know they've had a winter, so don't keep them too warm.
I wouldn't remove the brown leaves, let them be. At least until the new green leaves start to appear.