Hello Aline, happy to help.

I don't think your peace lily can be revived at this point. But to be sure, pull the plant out of the pot and check its roots. If it's a mass of mushy brown stuff, they were rotted by too much watering and there's nothing you can do.

If you see some firm healthy roots among those rotted roots, wash away the soil and cut off the rot. Then repot after cutting away all the dead stems leaving the remaining live (or almost live) leaves to help the plant regenerate roots. You may not see much growth activity for awhile while the plant grows more roots.

Also, find a suitably small enough pot to house the remaining roots -- ensuring there's an inch of soil space around the root ball. In other words, no need for a large pot. It would also help to pot it up in a terracotta pot because plastic holds water longer than a terracotta pot.

Good-luck!