In the predawn darkness on Feb. 24, Rinkel Kumari, a 19-year-old student from a Hindu family, disappeared from her home in Mirpur Mathelo, a small village off a busy highway in Sindh Province. Hours later, she resurfaced 12 miles away, at the home of a prominent Muslim cleric who phoned her parents with news that distressed them: Their daughter wished to convert to Islam, he said.