LONDON — A British neonatal nurse who was convicted of murdering seven babies and the attempted murder of six others has lost her bid to appeal. Lucy Letby, 34, had asked for permission to challenge the verdict after she was convicted and sentenced to life in prison last year. A three-judge panel of Britain’s Court of Appeal heard the case in April and released its decision on Friday. “Having heard her application, we have decided to refuse leave to appeal on all grounds and refuse all associated applications,″ Judge Victoria Sharp said.