Can't open rear passenger door from inside

[GG007]

Hi folks,
Helping my sister again with her 2007 Yaris hatchack which she just purchased used.

We can't open rear passenger door from the inside (when unlocked, obvioulsy). It opens from the outside.
Even when we toggle the lock (small black rocker with red on it below handle), it doesn't open.

As extra information, when we pull on the handle/lever to open the door, regardless of the position of the locking rocker, there is no resistance at all. Whereas the rear driver-side door handle offers resistance before actually opening the door, as one would expect.

Any ideas?
Cheers!
Gilles