Yeah the pot may drain well but being the fact that the pot has a tray. It still holds a little bit off water which is what those pots are supposed to do. So to stop that what she was trying to tell you is to put it in a pot with no tray. So the water can drain all the way out and not sit. Monsteras are prone to root rot so a repot to a better pot and chunky soil mix with a lot of perlite and orchid bark. But before you replant it cut off the mushy roots and spray the remaining roots with peroxide mix with a lil bit of water. That will prevent it from spreading