“Is speech therapy effective for late talkers?”

Speech therapy can definitely help and early intervention is so important! Close the gap before it widens. I recommend having your child assessed. According to ASHA, at 19-24 months your child should use and understand at least 50 different words for food, toys, animals, and body parts. Your child should put two or more words together—like more water or go outside.
https://shelsspeechbythebeach.com/

Yes! That is a large part of a Pediatric Speech Therapists job, is working with children who are late talkers. If shes two and not yet talking, I would recommend that she be evaluated by a Speech Therapist as soon as possible. :)