I'm not so certain. Jeantel called T back after the phone went dead. Why would she do that? The first reason that comes to my mind is that she was concerned for him as a friend and wanted to try to make sure he stayed out of a fight. The other scenario is that M doubled back and hid in the bushes ready to fight Z. I think it is more likely that M spent a few moments near the back of his father's girlfriend's home, but then turned back, either to do some more neighborhood casing, or to hide in the bushes and jump Z when he passed by.
When Trayvon was killed because of her she went dark until Benjamin Crump hunted her down and gave her a script to follow.
At face value Jeantel is a self described reluctant witness. I think one needs to consider that as a starting point for any of her presumed motivations. A lot of high powered adults and lawyers are flying around her, no doubt eager to have her testimony support M. Jeantel resisted by letting the world know that M was a homophobe. It seems a shame that so many on FR are judging Jeantel by her appearance, or by her speech, or her lack of education. In any case, people should be charitable.