At this point, I would say she knows him a lot better than she knows Barry.
I know that the original Post-COIE timeline has been partially redone, and Dinah is no longer a founder, but she still served with Barry for quite a while. She has known Wally for a long time, but he would have been "Roy's friend" or "Barry's nephew" until very recently. To my knowledge, this is the only iteration of the JL where they actually served together, and one of McDuffie's stories had Diana call him on the fact that he was never around. She never had the chance to really get to know him.
The real question is: why would Didio let Dinah approach Wally when she could be approaching the "iconic" form of the Flash?
For all we know Barry could be on Hal's team, so the "iconic" Flash would be taken.