5th Hokage Tsunade was in the ninja listing for months before she finally showed up in an event. It could be some time before GNW Sakura shows up as a log in reward. It's still possible for her to be April's log in reward; won't know until it's announced.

Sailor Sakura does show up in events to collect fragments from time to time, just like Sage Jiraiya. She'll come around again at some point.

All in all, it's just a matter of patience, really.