Chairman Mike Kelly said it was an “outstanding achievement”, adding that qualifying as a steam locomotive driver requires “enormous commitment, determination, skill and passion”.
“Steph has demonstrated all of those qualities throughout her journey,” he said.
“The ELR depends upon passing knowledge, skills and traditions from one generation to the next, and we hugely appreciate the dedication of all our volunteers who give their time and passion to keep our railway’s heritage alive.”
The ELR was closed to passengers by British Rail in 1972.
It was rebuilt later that same decade, continuing into the 1980s, and reopened between Bury and Ramsbottom in 1987. It was later extended to Rawtenstall and Heywood.
The 12.5 mile (20km) heritage route runs through the scenic Irwell Valley, passing through a landscape dotted with industrial relics, factories, fields and cottages.
It is a popular tourist attraction, particularly at Christmas when it operates the Santa Specials, and operates thanks to a team of more than 800 volunteers.