Peridot officially become Crystal Gems' member after she insult Yellow Diamond and refuse to help her! Garnet say Peridot is now Crystal Gems whether she like it or not!
Lapis is very hard to become Crystal Gems' member for 2 reasons
1. She despise Peridot for being responsible of bringing her back to earth
2. I think she doesn't know any Crystal Gems at all! Beside Steven! And she also Accuse Crystal Gems of trapping her even though Crystal Gems have no idea of her being trapped in a mirror but do know her name I think
What is take for Steven to get Lapis to join Crystal Gems?