Season 7: Zola Grey Shepherd
Six-month old Zola (Jela K. Moore) ends up at Grey Sloan to get surgery for her spina bifida. Meredith and Derek immediately fall for her and decide to adopt her. Meredith's tampering with her husband's clinical trial does create a rift between them and raise doubts for their social worker, but they eventually make up and get baby Zola back. Cue the happy tears!