I agree with the others, if WashU is your favorite, I would not applying binding somewhere else. Give it a shot.
I’ll add while your counselor might have better data, off hand I would say you still look like a reasonably strong RD candidate for Barnard.
And finally, there are other colleges I would consider similar in notable ways to WashU, and others similar to Barnard in notable ways, so those are really not your only chances for a great college experience anyway.