Eh, at this point you can only wait and hope. If Young Justice gets another book then shes a shoe in.
Until then.....Well she could still pop up in other things. We have three Wonder books coming this year on top of the Sensational digital first. Which is ALOT more than what Wonder Woman was getting prior to this.
Nubia went from being virtually a non figure in Wonder Womans mythos for fifty years to getting an OGN, and her own series.
Grace Choi had been all but forgotten but is now making a comeback.
Artemis after her five minutes of fame became a minor character in the Wonder Books until she was grabbed up for 'Red Hood and the Outlaws' and alongside Cassie shes being advertised as playing a part in the series to come.
Honestly its not like Donna is getting that much more than Cassie right now. Donna at present is one of twenty characters starring in the 'Titans Academy' book and isn't a central character in that title. But with all the positives that are coming Wonder Womans way the odds are good that we will see more of a push for her too.
Finally, I want to point out that Cassie could be in far worse positions.
Peng Deilan got a cameo in Orlandos run but hasn't been seen since and likely wont show up in the foreseeable future.
Maggie who was created in G Willow Wilsons run as a girl chosen by a magic sword to become one of the Amazons is standing on pretty shaky ground in terms of ever appearing again.
Akila went from being a Bana-Mighdall Black Panther to a murderous ex of Artemis' who had to be put down.
Cassie is not going to just vanish into thin air just because Yara Flor has popped up and is making herself known. She vanished when that new 52 run of Teen Titans ended and wasn't seen for years before Bendis picked her up for Young Justice. Yara is in no way a direct threat to Cassies existence.
If anything the existence of a Wonder Girl book gives Cassie far better odds of being seen again.