“I Am Your Woman” marked a major milestone for Syleena Johnson: It was the major-label debut single for the singer, then in her early 20s, and it was written and produced by R. Kelly, who had not only crafted his own No. 1 hits but also successes for Michael Jackson and others. That was in 2001, when dozens of artists wanted to sing songs written by R. Kelly and when Johnson could happily perform “I Am Your Woman.” Today, she can’t do it. And she won’t.