I think it was barely invented- not sure it was in use enough that she was tracked on it. According to this they were using radio bearings and a smoke plume...
https://news.nationalgeographic.com/2017/07/amelia-earhart-disappearance-theories-spd/
See my post 148. I read a very interesting book on her - included a lot of her early flights. The latter half of the book was about her round the world attempt. It seemed to be very well researched with lots of notes in the end of the book. I think they came up with several possibilities based on how flight worked at the time - but that she went down while doing a north-south search pattern looking for the island.