Velma Gwendolen looks very pleasing to the eye. It sounds nice too.
I also like
Velma Siobhán a lot.
Velma Marie flows worst bc of the -ma Ma- repeat.
Velma Jeanette and
Velma Jade make me want to suggest
Velma Jean. That flows well too.
Although it flows with
Louise I wouldn't combine it with
Velma, bc of
Thelma.