If you talk to Clemence he says that Alexius ordered all those without magical talent to leave Redcliffe. Clemence points out that even if they left one would have to wonder where they'd go, but just because Clemence points that out doesn't mean no Tranquil actually left.
After all, Tranquil end up becoming rather.... malleable, as Alrik's depraved acts demonstrated.
So factoring in that and Addai's posts on how many of the Tranquil were abandoned in the Circles, and IIRC Minaeve's comments, I see no reason to cast blame on Fiona for the Tranquil not being there, especially since we have no idea how many she had with her in the first place
And also since there are only like... six Oculara in the Hinterlands and they're scattered about.
Granted, it doesn't mean I won't call out Fiona for being a ******-poor war leader in the game as it stands. Tranquil are useful. A lot of what she did makes me question her capability of being a war leader. And a lot of that also makes me question whether Bioware even cares at this point to make wars be depicted as they should be or if they use them more for shock value.