dp/defo...my mistake?

[Little Jimmy]

This happened last night and no one complained but I think I was wrong. ASA womens fastpitch. Coach says dp is going in for defo(who was pitching). After a few batters I realize that DP is actually playing left field and former left fielder is now pitching. Game ends a few pitches later.

I know that dp can play defense for any player but when dp subs for defo(the pitcher) does she have to go in at the pitching position? Did I blow that one even though no one noticed?