According to the message, Lisa's cat (Tatze) has given birth to 3 kittens ("3 Junge bekommen"). So you can congratulate your friend on the birth of 3 new baby kittens. However, I notice that this message is actually from your friend telling you about Lisa's cat having kittens - it's not your friend's own cats. Your friend is just sharing the news and expressing that she wishes she had a cat too ("Ich will auch eine Katze").