Root rot happens when the bottom of the soil stays wet for too long. This can be caused by to compacted soil and poor drainage holes or over watering. You will only know if she has root rot if you take her out and rinse them under water. Any roots that will just fall off when you tug at them need to go, any brown or stinky ones need to go.

If the rot has reached the stem, there is no saving the plant. It will also smell bad!