Q.How tall does a elephant ear plant get?
My sister lives at Forest Hills, KY 41527 She has an Elephant Ear plant that is taller
than the house. I assume it is a perennial. She said it was there when she moved
into the house, which belonged to a mother 1n-law who passed away. Can you give
me some info on this plant.

Most are not very hardy, but some are. It sounds like the one planted there is. This will be very easy to care for, as there is not much that will need to be done. Since it is hardy to the area, you will not need to dig it up, unless you just want to divide it to give to others. Unfortunately, some varieties can get well over 15 feet tall, while others remain below a foot tall. It would be hard to tell you what type it was. By now it should be to its mature height by this time of year.
This article will help: https://www.gardeningknowhow.com/ornamental/bulbs/elephant-ear/growing-elephant-ear-plants.htm