It surprises me to hear "old lady tennis" being used to refer to poor movers. I'd have thought "old lady tennis" meant something more like a player whose game is either more cerebral or more consistent and reliable, and is not based on power. Hingis was an extremely cerebral player, as was Evert. Evert and Austin were also extremely steady, consistent, and reliable. None of them was a powerhouse. That's why I thought they would be described as playing old lady tennis, if anyone was.
I think that Venus was an extremely good mover, in her day. Both she and Serena sometimes had dodgy footwork early on - that's why Serena had a good rivalry with Capriati, for a while, as the latter was sometimes able to exploit her footwork - but they were very fast around the court.
Almost all players have more "devastating" forehands than backhands, but I'd still say that Venus's signature groundstroke was her backhand.