female dog that licks my other females ears and licks her butt

Question
I have 3 dogs. 2 goldens and one mutt. My oldest golden cleans the other goldens inside the ears. That is not a problem but as of lately she has started licking the other dogs privates. She just started this behavior 3 months ago.
Why is she doing this?  We yell at her to stop adn she does listen but she goes back to the other female and justs licks licks and licks. What is wrong and how can we stop this behavior

Answer
This is actually normal and thats how wolves greet but it can be annoying

The best way to get rid of the problem is to 'flick' the dog on the nose with your fingers and and 'awww aww' sharp and loud and that usually stops the problem after doing that a few times