Melinda Heather "Mindy" Cohn was a natural choice to be Velma's voice from 2002 to 2015. That's because her natural voice is perfect for the part of Velma.
From August 24, 1979 to May 7, 1988, NBC's audiences heard Mindy's voice on a weekly basis as she starred in the TV sitcom The Facts of Life.
Mindy is Velma the College Graduate because she is Velma's voice in the movie Scooby-Doo! in Where's My Mummy? At the end of the movie, Velma mentions something that she did while in college.
Mindy herself has Bachelor's degree in Cultural Anthropology.
Prior to the airing of the TV movie The Facts of Life Reunion (2001), the ABC TV network released a press kit which describes how Mindy got into acting:
"Mindy Cohn made her acting debut as the witty, outspoken Eastland Academy student, Natalie Green, in the hit comedy series The Facts of Life. She was discovered while attending Westlake School for Girls in Bel Air, California, when actress Charlotte Rae and producer Norman Lear came to the school to authenticate scripts for their new show. Ms. Rae was so taken with the vivacious eighth grader, she convinced producers to create a role for her. Ms. Cohn remained on the show for nine years, then traveled to Paris and Australia with her co-stars to produce two successful television movies based on the series."1
Information Source:
1The Facts of Life Reunion. ABC Press Kit. Retrieved from http://www.televisionhits.com/factsoflifereunion/presskit.html