Based on what your friend said, Lisa's cat (which is referred to as "ihre Tatze" in the message) gave birth to 3 kittens. So you can congratulate her on the arrival of the three new babies. Here's an example congratulations message in English: "Congratulations on the arrival of Lisa's three adorable kittens! They look so cute in her Instagram post. I can see why you want a cat too!" And here's the same message translated into German: "Herzlichen Glückwunsch zum Nachwuchs von Lisas Katze! Die drei süßen Kätzchen sehen auf ihrem Instagram-Post aus. Ich kann verstehen, warum du auch eine Katze haben möchtest!"