My 13-month-old border collie has great recall in the yard but at the dog park she ignores me completely. She'll play with other dogs for 30 minutes straight an

Nothing's wrong — the dog park is more interesting than you. Your yard recall is untested because there's no competing motivation. You built the skill in easy mode and deployed it in impossible mode. Start over in environments with medium distractions. Practice at a quiet park on a long line (30 feet). Let her sniff or watch other dogs at a distance. Call her once using a high-value word (not 'come' if that's been poisoned by overuse). If she doesn't turn toward you in 3 seconds, reel her in with the line and reward her anyway when she reaches you. You're teaching the pattern, not testing compliance. Do this 50 times across two weeks in progressively harder environments. Then try the dog park on-leash first. Call her when she's between play sessions, not mid-chase. Reward with something better than what she left — tug, a game, a jackpot of treats. If you only call her when it's time to leave, she'll learn that recall = end of fun. Call her 5-6 times during the visit, reward her, then release her to play again.