Rora being The Mole for Dirim's side while she was with our heroes makes perfect sense in hindsight when you take into consideration several small details in the episodes leading up to and after Episode 16:
There's mention in Episode 12 of someone tracking the group and they never succeed in finding out who it was. Less than a few episodes later in Episode 16, Rora conveniently shows up and saves Ellers and Hana, despite the fact that she wouldn't have any reason to be there and the fact that no one else knew about their little sidequest...unless she was already following them.
The two episodes after Episode 16 also mention a group trying to get at Eric and James starting from Redridge, and the end of Season 1 has this group (led by Big Bad Dirim) know they were headed to Moonglade to try to get them out of the swords, and successfully orchestrate a kidnapping just mere seconds after Tanaris is mentioned as the heroes' next destination. Again, despite the fact that the heroes never let anyone of significance know about their quest, they were somehow found out in a small enough span of time for Dirim to find them... unless you take into consideration who joined the group prior to these details being revealed: Rora. A hunter, a class known for their tracking abilities. She would have had little difficulty finding their location even with their small group size, and given the possible theory below...
Now of course the next big question is how did Rora tell Dirim about the heroes' movements without being noticed? Episode 27 reveals that Dirim has magic rings that cannot be tracked magically, and are inconspicuous enough that no one would really notice them being used unless you knew what to look for. It's not a huge stretch to assume that Rora likely had one of these rings from the get go before joining up with the heroes, to better keep track of them and keep Dirim aware of their movements.
Finally, it's notable that in Episode 31, where Dirim's true nature is revealed, he oddly enough chooses to leave a portal behind under the pretense of following typical Supervillainy, and also to taunt the heroes into pursuing him. It ends up having a much more important reason considering who's the first person who goes after him: Rora. Dirim wasn't leaving the portal behind only for the sake of villainy, but also to give his spy a chance to join up with him without the heroes realizing it.
