Based on what your friend said, it seems that Lisa's cat had 3 kittens. She mentioned "3 Jungen" which translates to "3 male offspring" in English. So the cat gave birth to 3 baby boys. You can congratulate your friend by saying something like: "Herzlichen Glückwunsch! Ich freue mich für dich, dass du so lange auf dieses Ereignis hoffen durftest." Or simply: "Viel Glück mit den neuen Jungen! Ich freue mich schon auf die ersten Fotos." I would avoid spoiling the surprise if she hasn't told you directly yet. But based on her excited post, it's safe to assume she'll be thrilled by your kind congratulations on the new kittens.