Based on the message, your friend is referring to someone named Lisa whose cat ("Tatze") has given birth to 3 kittens ("3 Junge bekommen"). The message is in German and says that Lisa shared this on Instagram, and the kittens look very cute. Your friend is expressing that she also wants a cat. So to congratulate your friend, you'd be congratulating her on her friend Lisa's cat having 3 kittens, not on your friend having babies herself.