You could consider asking both folks to write you letters, and either (as mentioned above) submit both if 4 would be allowed, or send the lab coordinator's letter to more research-heavy sites, and the Psy.D.'s letter to more balanced or clinically-leaning sites.
That being said, I'd be a little surprised if many programs would hold your letter writer's degree (Psy.D. vs. Ph.D.) against you. I'm sure it's possible, but I would hope the vast majority of programs wouldn't do so. As neuronic said, what's going to be more important is how strong the letter is overall, and how personal/individualized the writer is able to be.