Teaser 2901: Square deal

From The Sunday Times, 29th April 2018 [link]

George and Martha have five daughters who have periodically appeared in my teasers over the years. They are all working for the same company and have perfect-square four-digit telephone extensions, in all five cases. The letters ABCDEFGHIJ stand for the digits 0-9 but in no particular order. The extensions are as follows:

Andrea = IBHC
Bertha = DJJC
Caroline = BAFH
Dorothy = GFID
Elizabeth = GAEE

What are the five extensions?