The young Velma Dinkley, in A Pup Named Scooby Doo, was voiced by Christina Lange. This was the only Scooby series for which she provided work, therefore, Lange's work was from 1988 through 1991. During this series, Velma was portrayed as a child or preteen (never really sure about ages). In the series she walked a lot like Marvin the Martin and carried around a computer.
The majority of Lange's body of work is outside of Scooby. As far as voice over animation work, Christina Lange was the voice of Raggedy Ann in the 1988 Adventures of Raggedy Ann and Andy, Sister Bear in the Berenstain Bears, and Wendy in the 1990 Peter Pan and the Pirates animated series. She is also did some acting, but she never acquired a recurring role on any show.