If you were a political group taking hostages and facing severe backlash, it would be to your advantage to treat the ones you plan to release very well for PR credit. Especially after a violent massacre of innocent civilians when you badly need positive perception. Additionally, releasing older women seems like an easy choice, since society will see you as having a conscience since they are one group of weaker members.

But this isn't such a significant moment. The sobering reality is the elderly have less utility as hostages, so it's no loss from the Hamas side. We also know that during her abduction the treatment wasn't all positive. And without information on the status and treatment of the other 200, which based on human history I can assume doesn't perfectly follow the story here, this release means very little from the larger view.